Scottish Premiership: What did we learn from the weekend's games?
Rangers strike a big blow in the Scottish Premiership title race, Motherwell are stunned by Hamilton Academical and Hearts fall further behind at the bottom despite a first point under Daniel Stendel.
Steven Gerrard's men earned a first Celtic Park victory in nine years and are just two points behind the league leaders with a game in hand.
Kilmarnock have now gone six matches without scoring, Aberdeen drew with 10-man Hearts, Ross County claimed another point on the road but Hibernian fell flat after their Edinburgh derby victory.
Here are the top takeaways from Sunday's Scottish Premiership...
Celtic need to rediscover tactical derby edge
In the past two Old Firm derbies, Celtic have been found wanting tactically. In Sunday's 2-1 defeat by Rangers, the champions were once again swamped in midfield and struggled for width as they resorted to long balls towards Odsonne Edouard under pressure from players in blue.
It was the same story in the League Cup final - which they remarkably went on to win - earlier this month and in the two defeats last season at Ibrox. They were brilliant in the 2-0 win in Govan back in September, when they proved they do have the nous to execute a bespoke game plan to best their city rivals. But unless they rediscover that authority and ability to get their best players in positions to influence these crucial matches, they might find the tantalising prospect of nine titles in a row slipping away.
Rangers jump another psychological hurdle
Anyone who described Gerrard and his players' post-match celebrations at Celtic Park as over the top hasn't been paying attention. Even as things have improved in the former Liverpool captain's 18-month in tenure, there have been speed bumps, a lingering sense that his team have a way to go before finally winning something.
On no occasion was that more evident than the League Cup final, where they dominated Celtic but still contrived to lose. It was seen as an illustration of the difference in the sides' mentality.
But though Rangers do stumble, they always seem to show they are learning in the process. Since that final loss they have won every domestic match - culminating in Sunday's brilliant Old Firm triumph - and qualified for the last 32 of the Europa League. The next step is to pick up where they left off after the winter break. Last year they lost the first league game back to Kilmarnock and ceded the momentum they had gained in beating Celtic for the first time in 12 matches.
A first league win at Celtic Park since 2010 was a statement and they are now just two points behind with a game in hand. Can they learn another lesson and back it up after the break?
Motherwell rue missed opportunity
This defeat may well linger in the consciousness of Stephen Robinson for some time.
With Aberdeen being held at Tynecastle earlier in the day, a four-point gap could have been carved open to cement third spot ahead of 2020. Instead, the gap sits at one and Motherwell will still be shell-shocked at how this one slipped away as they step on the flight to Tenerife.
In front after five minutes and in firm control, they simply couldn't cope with a resurgent Accies who outfought, out-jumped, outran and outworked them.
Motherwell finish the year still in third - and third across the whole of the calendar year - so there is plenty to be celebrated. If they wish to stay there, this type of performance must be cut out.
Aberdeen squad needs freshened up
Inconsistency has been the mark of Aberdeen's season and Derek McInnes will have breathed a sigh of relief when he heard that Hamilton had come from behind to beat Motherwell and ensure his side are only a point behind the Steelmen in the race for a Europa League spot.
The disjointed Dons were second best for most of their 1-1 draw with a Hearts side who had previously lost five in a row, and only came to life after Sean Clare's red card allowed Niall McGinn to curl in the equaliser.
McInnes had already stated that he will look to freshen up his squad during the January transfer window and that will be hastened by a recurrence of on-loan Bristol City utility man Zak Vyner's shoulder injury.
Livi hit form at perfect time
After a poor run of form in which Livingston went eight games without a win, they have well and truly turned a corner. In December they have lost just once in six, picking up three wins in the process.
The impressive home form that allowed Gary Holt's side to punch above their weight last season is clear to see again. Sunday's clean sheet against Hibs means the West Lothian outfit have conceded just two goals in their past seven home matches - keeping six clean sheets - and it is this kind of form and resoluteness that will have Livingston going into the winter break feeling they can rise higher than last term's impressive eighth-placed finish.
Holt will surely have ambitions of finishing in the top six.
Ross must address Hibs' soft centre in January
After Boxing Day's derby win, Jack Ross would have been expecting his side to kick on in the final game before the winter break.
What he got instead was a toothless performance and yet further evidence of the soft centre that plagues Hibs, as they failed to impose themselves on a scrappy game.
This will surely be an issue Ross will be eager to address in January. He may even question why hulking defensive midfielder Marvin Bartley was let go in the summer, given his impressive displays for a Livingston team that beat Hibs so comfortably on Sunday.
Killie need 'shaken up'
Caretaker manager Alex Dyer made it very clear at the end Sunday's 1-0 loss to St Mirren that Kilmarnock need to appoint a new manager as soon as possible.
Dyer spoke about the club losing its identity. He was assistant to Steve Clarke when they were extremely hard to beat, coherent and ruthless in attack, claiming a number of big scalps and back-to-back record top-flight points tallies. He feels the core of that team is still there, but that one or two will freshen up the squad.
"We need a few recruits to give the place a lift," said Dyer. "Whoever is in charge, whether it's me or someone else, someone needs to come in and shake the place up."
County keep scraping points on the road
While Ross County weren't particularly impressive at McDiarmid Park, Stuart Kettlewell and Steven Ferguson will be pleased to have earned a point they probably did not deserve.
The Highland side have made a habit of picking up results on the road this season. So far they have won 2-1 away to Motherwell and picked up draws at Hearts, Kilmarnock, Hibs, Hamilton and now St Johnstone.
That may not seem like an impressive list of results, but when it comes to points won on the road Ross County currently sit seventh in the league table - and have picked up twice as many points away from home as St Mirren, who are two places behind them.
Performances like Sunday's may not rouse the County support, but could play a vital role in preserving their top-flight status.
Lack of firepower holding Saints back
St Johnstone should have picked up all three points. Manager Tommy Wright said as much - as did County co-manager Kettlewell. Yet the team were held back by a simple but vital problem: they simply don't score enough goals. Although the Perth side managed 15 attempts, only three were on target and ultimately a lack of ruthlessness proved costly.
So far this season, the Perth side have only mustered 16 goals from 19 games. Not only is that the worst record in the top flight, but it also undermines a defensive record that has gone a long way to turning around their overall form.
Just three clubs - Celtic, Rangers and Motherwell - have conceded fewer goals than St Johnstone in the past 10 match days, yet that impressive stat only goes so far if the players at the other end of the park are not firing.
St Mirren living dangerously
Sunday's 1-0 win over Kilmarnock was one of St Mirren's best performances of the season. Manager Jim Goodwin suggested his side probably created more chances than in any other game.
After Ilkay Durmus' early goal they had numerous opportunities to post a much more comprehensive win. Junior Morias had two good chances, Jonathan Obika three. Tony Andreu had a header saved and Durmus could have doubled his tally.
Just one chance was all Kilmarnock needed to salvage a draw. St Mirren got away with it, but in the cut-throat fight against relegation they can seldom afford to be so profligate.
Accies show seasonal improvement
This time last year Hamilton, the top-flight's sense-defying escape artists, had 14 points. Despite that poor tally, a further 18 were added in the second half of the campaign to secure their safety for another season.
Jump forward to the present, and victory over Motherwell nudged the tally for the current campaign to 18 points. Not a huge increase, granted, but enough to hint that the South Lanarkshire side keeping their Premiership status is a fair bet again.
Facing near rivals Motherwell they were dominant after going behind with an inevitability about their first away win of the campaign. It's not always pretty with Accies, but they have a habit of hanging in games, and that could well save them.
Stendel needs quick turnaround
Daniel Stendel is only five games into his tenure as Hearts manager but will realise he is running out of time to arrest his team's decline fast enough to save them from relegation.
With veterans Glenn Whelan and Christophe Berra dropped for the visit of Aberdeen, along with experienced summer signing Aidy White, the German seems to have a ruthless streak as he looks to introduce more "leadership" and youth to his side.
However, despite showing some signs of improvement as they earned their first point since he took over, they find themselves further adrift at the foot of the table after the two clubs above them both won, and his promised new signings will need to hit the ground running when the Premiership resumes.