In his regular BBC Sport column on football tactics, Robbie Savage takes a closer look at West Ham's comeback to beat Chelsea 3-1.
West Ham were outplayed in the first half at Upton Park and were lucky to only be 1-0 down at the break.
Hammers boss Sam Allardyce made important substitutions at half-time that helped to change the game, bringing on Mohamed Diame and Matt Taylor.
But the key to his side's victory also lay in the way he tweaked his tactics at the same time, and the effect they had.
SECOND BALL KEY TO SECOND-HALF DISPLAY
West Ham were getting over-run before half-time.
Chelsea were winning the first and second balls every time West Ham knocked the ball forward and, when the Blues attacked, they were finding big gaps in the Hammers midfield.
What Big Sam did to change that was to push his wide men, Matt Jarvis and Taylor, higher up the pitch.
The reason he did so was to get men nearer to Carlton Cole, and also because it allows the whole team to move up too.
It had a knock-on effect because the gaps between Cole up front, the midfield and the defence became smaller, which meant they started winning the second ball a lot more often, putting them on the front foot.
The second ball is so important in football, in every area of the pitch.
Cole was never going to beat Branislav Ivanovic every time the ball was played up to him, but what changed was that, when he didn't, there were other West Ham players near enough to pick up the ball and continue the attack.
It helped defensively too. James Tomkins had huge areas to cover before half-time, between his defence and midfield, and he was often isolated.
Because West Ham were playing in Chelsea's half after the break, Diame had much smaller areas to cover when he replaced Tomkins. Just as Cole had Jarvis and Taylor nearer him, Diame had Kevin Nolan and Mark Noble.
Diame clearly played a big individual role - he made a lot of key challenges himself and covered a lot of ground - but the other difference was he had help to ensure Chelsea could not just pass round him like they had been doing.
The spaces that Chelsea were exploiting before half-time were not there afterwards.
You could see that for West Ham's third goal. Diame chases the ball and closes down Ashley Cole to put him under pressure, but there are other Hammers players around him to force the mistake too.
All of this happens in Chelsea's half.
LONG BALL NOT THE ONLY OPTION
Allardyce is often criticised for his long-ball tactics but it is absolute nonsense to say he is a one-trick pony.
In Andy Carroll or Carlton Cole, West Ham have got the outlet of a big centre-forward to provide knockdowns for Nolan to ghost into the box and get on the end of, so of course they are going to play to their strengths occasionally.
But they have ball-players too, like Noble and Jarvis, and they also mix up their approach, which is an even better sign of a manager's tactical nous - because some sides do not have a Plan B.
In the Hammers' case, if Plan A is a direct ball for Nolan to feed off, then Plan B is to get on the ball and pass it around.
I wrote recently about how Sunderland contain all the usual hallmarks of a Martin O'Neill side, even if they are struggling for form.
Well, this Allardyce team is typical too. When I've played his sides in the past, they have always had flair players - at Bolton it was Jay-Jay Okocha and Youri Djorkaeff - as well as a target man like Kevin Davies.
As I have already mentioned, with the Hammers, he has got Jarvis and Noble who can open sides up, Nolan to go up and down and Carroll or Cole to aim at.
But you can forget about the Allardyce stereotype of hoofing it up the pitch.
West Ham will play it around and get it wide to give it to people like Jarvis who are good on the ball because Sam knows they will give the right service to the men in the middle.
You could see that against Chelsea. Balls in from Jarvis out on the left led to West Ham's first two goals.
HARD TO STOP BIG SAM'S SYSTEM
When I came up against Allardyce's Bolton team as a player, I always knew I was in for a hard game against a team that would work hard for their manager and be well organised tactically.
You always knew you would have to work hard and play well to beat them.
To win, you had to be aware of their threats - from set-pieces for example - but also concentrate on your own system. If you tried to play them at their own game, you would lose.
Stopping them was difficult, though.
From my point of view as a defensive midfielder, it was always tricky to know how to deal with Nolan, even when you knew what he was looking to do.
As an individual player I would always look at who I would be up against and think about how to get the better of him but, when it was Nolan, he found areas that made it difficult to follow him in to.
For example he would never track me all the way back when I went forward - instead he would just hold his position and make me think about whether to gamble and run into the Bolton box or sit in, because I was worried about him being behind me.
His movement meant it was difficult to know who should pick him up too. If we were playing with four at the back, then my two centre-halves often only had one striker - Davies - to mark.
So, when Nolan got forward to support him, I would think 'right, he becomes my centre-half's job now'. I would concentrate on Gary Speed or Okocha, or whoever else was in their midfield.
That uncertainty on who is marking him is what Nolan thrives on, and he is obviously an important element of Allardyce's team.