Arsenal played well and showed great character with 10 men against Chelsea, but taking striker Olivier Giroud off after 22 minutes was a mistake that cost them the chance to get something from the game.
Gunners boss Arsene Wenger had to sacrifice an attacking player to bring on another defender when Per Mertesacker was sent off for a professional foul, but I think his choice shocked everyone.
The Arsenal fans and Giroud himself made it very clear what they thought of the decision, and I agreed with them.
I can honestly say I have never seen that happen in any game I've been involved in. If a team has a defender sent off, it is usually one of their 'luxury' players who gets dragged off - not the big striker.
Without Giroud, Arsenal had no focal point for their attack
Personally I would have taken off Joel Campbell, but I would also have chosen to lose Mesut Ozil or Theo Walcott rather than Giroud.
It was 0-0 when Wenger made the switch and it is possible he was already thinking he would take a draw, but he must surely have been thinking that he might need a goal at some stage.
If Campbell came off and Arsenal conceded quickly as they did, Wenger might have regretted his decision but he had another similar player in Alexis Sanchez on the bench who could have come on to try to rectify the error.
The main problem with taking Giroud off was that Arsenal did not have another striker like him. Once Wenger made that decision, then tactically he was totally committed to playing one way.
In effect, it meant Arsenal were playing without a centre-forward because Walcott stayed out on the left when Giroud went off.
Ozil was their most advanced player centrally from the 22nd minute onwards, and he only touched the ball in the Chelsea box twice - he was clearly not going to act as a focal point for their attack the same way Giroud would have done.
That was one of the reasons Arsenal had so few shots, and took until the 86th minute to get one on target, because the likes of Ozil and Aaron Ramsey were trying to get past defenders to shoot on the edge of the area rather than running on to something that Giroud had teed up for them.
Walcott's pace always less likely to work
Arsenal taking off Giroud was like Manchester City taking off Sergio Aguero in that situation - someone who is their main goal threat and their top scorer this season.
I would argue that, when you are down to 10 men, Giroud brings more to the table in every area than a striker like Aguero because, not only is he dangerous in open play, he is an asset at set-plays too.
Defensively, Arsenal had just lost Mertesacker, the tallest player on the pitch and Giroud would have given them additional cover in the air at the back.
Then there is what he offers Arsenal when they have corners or free-kicks in attacking areas, or when Mesut Ozil gets on the ball out wide and whips the ball across the goalkeeper for Giroud to get on the end of it.
A striker like Giroud allows your team to get up the pitch, sometimes regardless of the quality of the passes he is getting, because of his presence.
As a midfielder, it was always easier when I had someone of that stature to aim at when we were a man down, to hold the ball up and take fouls that give you set-pieces.
I could see Wenger's thinking when he explained afterwards that he wanted to use Theo Walcott's pace instead but, to me, that approach always seemed less likely to work.
Two of Chelsea's defenders, Kurt Zouma and Cesar Azpilicueta are very quick and to beat them that way takes the perfect pass. Walcott did get behind them, twice, but on both occasions he was offside.
Arsenal wobble no cause for concern
Arsenal's defeat means they have only taken two points from their last three games, but I do not see their recent form as real cause for concern for their title hopes.
Gunners fans will be worried, of course, because of their side's recent history of falling short in the latter stages of the season.
But I would focus on the performances they have put in against Liverpool, Stoke and now Chelsea, rather than the results.
Wenger will not be happy with the way they conceded on Sunday, but I think he will be proud of the way they responded and the effort his players put in. Chelsea were hanging on at times.
Yes, Arsenal's second home league defeat of the season was a set-back but they again showed the kind of character they will need over the next four months.
The way they have responded in tough situations, to draw at Anfield and the Britannia Stadium - and fight with 10 men against Chelsea - is a sign they have the mental strength to be champions, and I am standing by my prediction that they will win the league.
Jermaine Jenas was speaking to BBC Sport's Chris Bevan.