Not too long ago, it looked like West Bromwich Albion and Leeds United were going to have promotion to the Premier League sewn up in near-record time.
However, a run of just two wins in their past 15 combined matches have set nerves on edge in the West Midlands and West Yorkshire.
What's gone wrong? And what do they need to do to get back on track in the race for automatic promotion from the Championship?
14 December - The turning point?
West Brom: Two late Charlie Austin goals saw Albion battle back from 2-1 down to claim a dramatic late win at rivals Birmingham City.
But the victory came at a cost, with West Ham loanee Grady Diangana forced off with a back injury.
They have not won in the league since.
The 21-year-old forward had five goals and six assists in 19 league appearances before his injury and came back into the starting XI last Monday against struggling Stoke.
Four minutes into the game he was forced off with the same back-related hamstring issue and the league leaders went on to slip to a lacklustre 1-0 home defeat.
To make matters worse, fellow loan star Matheus Pereira will now serve a three-match ban after being found guilty of violent conduct in that game.
"The loss of Diangana is two-fold really, as it's also coincided with a dip in form for their only other real playmaker in Pereira," BBC WM's Albion commentator Rob Gurney told BBC Sport.
"The pair often seemed on the same wavelength, almost anticipating what the other was going to do.
"Pereira seems to be feeling the loss most keenly, and Diangana's withdrawal just a couple of minutes into the Stoke game floored everyone - the fans inside The Hawthorns and his team-mates."
Leeds: Hours after West Brom's dramatic win, Leeds were enjoying a far more serene afternoon at home to Cardiff.
With 30 minutes of their home game against the Bluebirds to play, Leeds were 3-0 up and looked set to extend their lead over third place to 12 points.
A crazy finale saw the visitors score three times, despite having a man sent off with five minutes to go, to draw 3-3.
Since then Leeds have won just one of six league games, while their previously watertight defence has shipped 11 goals in that time.
"Nobody saw that result coming. At 3-0 up we were so comfortable I thought we'd score another," BBC Radio Leeds summariser and former Whites forward Noel Whelan told BBC Sport.
"That Cardiff game highlighted the frailties and weaknesses we have against defending balls from wide areas and set pieces.
"We crumbled in the last few minutes and it was quite shambolic. I said after the game that it was naive and it dented confidence."
He added: "We had such a comfortable gap of 13 points at one stage but we've seen from the teams below not getting results that the pressure is on everyone, not just us.
"They're still in a commanding position. The gap has closed, but Leeds' destiny is still in their hands."
West Brom: Former Croatia and West Ham boss Slaven Bilic arrived at The Hawthorns in June, three months after previous Albion boss Darren Moore was sacked.
After a solid start to the season, a run of six successive wins between 4 November and 8 December cemented their place at the top of the table.
The 51-year-old appealed for calm after the defeat by Stoke and with some justification. Third-placed Fulham are still four points behind, plus the Baggies have a game in hand.
"A mini-crisis, yes. Hard times, yes. But we knew it was going to be no easy ride," said Bilic. "We are still top of the league. We have to embrace the challenge and show the right character."
Gurney added: "He called for unity after the Stoke defeat, and told me it was no time to 'go into a corner and cry' - clearly one of the themes of his post-match debrief before coming out to face the media.
"The respect the players have for him is clear to see; it's time they started delivering again."
Leeds: Marcelo Bielsa is having a second go at getting Leeds back into the Premier League after a late-season slump last campaign cost them automatic promotion, before an action-packed play-off semi-final against Derby ultimately went the way of the Rams.
Like Albion, Leeds enjoyed a brilliant November, winning seven games in a row between 2 November and 10 December to go 11 points clear of third place.
Fans have sometimes questioned whether Bielsa's high-pressing, high-energy football can work across a 46-game league season when the Argentine also believes in using a streamlined squad.
Only Millwall (22) have used fewer players in the league this season than both West Brom and Leeds, who, along with Sheffield Wednesday, have used 23.
"Marcelo does not like to change, that is how he works. If plan A isn't working then do it better," Whelan said.
"The fans have said about the players being tired but you look at Liverpool, who play in a similarly high-pressing style, and they're not burnt out.
"Some of the football that has been played by Leeds, at the tempo it has been, has been amazing to watch. In the first half of the FA Cup tie against Arsenal we made them look like the Championship team. It's just the cherry on the top that's missing."
How do they put things right?
West Brom: "Defending set-pieces better is the number one priority at the moment - no clean sheets at home so far this season, for a team at the top of the table, is a pretty amazing stat," Gurney said.
"Poor defending at set-plays hasn't been entirely to blame for that record, but the part-zonal/part-man marking system Bilic has been using continues to have issues. Are the players properly buying into it?
"Most transfer talk has surrounded the Croatian forward Mislav Orsic, at Dinamo Zagreb, of whom Bilic is a self-confessed fan.
"When I suggested they looked like a side that needed freshening up after the Stoke defeat, Bilic said: 'I hope we're going to do it as soon as possible'."
Albion are the division's leading scorers so it might seem strange to say they could do with finding a player they can rely on for goals. However, six of leading goalscorer Charlie Austin's seven league goals came in a five-game stretch in November and December.
Perhaps Saturday's FA Cup fourth-round win at West Ham will provide the impetus they need.
Leeds: As with last season, creating chances is certainly not a problem for Leeds - but the issue of making the most of them certainly is.
Patrick Bamford has already hit double figures but he has taken 80 shots for his 10 goals, while the league's top scorer, Brentford's Ollie Watkins, has scored 18 goals from just 55 attempts.
RB Leipzig striker Jean-Kevin Augustin has arrived on loan until the end of the season, while Manchester City winger Ian Poveda has joined on a long-term deal.
Both players will be under pressure to perform straight away as Leeds look to end their 16-season spell outside the Premier League.
"It's no secret that we needed a striker in. I love Bamford for what he offers the team and how he has improved here, I think he'll get to 20 goals this season, but he needs help," Whelan said.
"You can not go through a whole season with just one or two strikers in the Championship because it is such a demanding league."