In any big encounter you will often hear managers say it is the "fine margins" that decide a game of football.
Sometimes it is luck. Sometimes it is individual brilliance. But on Saturday it was Sonia Bompastor's bold decisions that helped Chelsea beat Manchester City 1-0.
The top-of-the-table Women's Super League clash was as intriguing as you would hope it to be and both managers needed to be on their toes.
Chelsea boss Bompastor "took responsibility" and brought off struggling defender Kadeisha Buchanan 12 minutes in, and it had the desired effect.
City striker Khadija Shaw was not able to get in behind like she had done in the early stages, and Buchanan's replacement Veerle Buurman shone.
Was it a tactical substitution or was Buchanan injured?
When the fourth official's board went up showing the number of the player Buurman would replace, there was confusion from Chelsea players.
It was clearly not planned, nor had Buchanan asked to come off. There was no apparent injury as she jogged off and she was clearly upset, heading straight down the tunnel.
Asked to clarify the situation, Bompastor said: "Yesterday in training she got a knock to her head in contact with a team-mate but she was fine.
"She was fine in the evening and we assessed her again this morning and everything was fine. I had that information before the game.
"But I felt from watching her at the beginning of the game that she was not herself. I took the responsibility to make the substitution.
"I felt I was almost forced to do that. I know my player and she was not in the game."
Whether Buchanan's shaky start was down to that knock is unclear, but Bompastor knew her decision was a risk and was willing to act immediately.
Buurman instantly marshalled Shaw, and City's early threat was quietened as Chelsea regained control and ended the half a goal up thanks to Sandy Baltimore.
Shaw did not record a shot on target and in-form England international Lauren Hemp was quiet as Buurman performed well in a stubborn Chelsea backline.
City manager Andree Jeglertz said he did not think the switch "changed the picture", but he was outsmarted by Bompastor during the 90 minutes.
Bompastor admitted she had not spoken properly with Buchanan at full-time but promised to "explain myself to her".
"I just told her a few words. My assistant coach Camille Abily will have done that already probably and I think everything will be fine," said the Frenchwoman.
"I always have good relationships with the players, bring them clarity, and I'm always direct and honest so they have the information. It won't be any different."
The risky substitution was compounded by an injury to striker Melvine Malard 23 minutes later, meaning Chelsea's XI was tweaked twice before half-time.
Not normally one to bring on players at the break, Bompastor was smart and hooked goalscorer Baltimore, who was likely still buzzing from her impact.
She was replaced by Maika Hamano, who went on to play the ball through to Alyssa Thompson when she was brought down by City goalkeeper Ayaka Yamashita, and she was shown a straight red card as a result, ending the visitors' comeback hopes.
"We knew going into the second half we only had one substitution slot and we knew Sandy has been playing lots of minutes," said Bompastor.
"I knew she probably didn't have the legs to go more than maybe 60 minutes and I knew I didn't have more slots after that. I was forced into this one as well.
"It paid off and that's good. Sandy was doing well but she knows the reason why we made that decision.
"That's the first time I experienced that kind of substitution in the first half. It's good for my own experience."
Bompastor's bravery was rewarded and, while City certainly had their chances, Chelsea defended resiliently to see out the narrow win.
Jeglertz could not find a solution to Chelsea's attacking threats, which came largely from wide areas via Ellie Carpenter and Thompson.
Vivianne Miedema returned from injury and looked sharp when she came on for City in the second half, but it was not enough to change the result.
In contrast, Bompastor's risks proved the difference, and they were made with former Chelsea boss Emma Hayes, who mastered the art of bullish decisions, watching on in the stands alongside Sarina Wiegman at Stamford Bridge.
Chelsea's victory bumped them back up to the WSL summit, a point above City, while Buurman picked up the player-of-the-match award.
"It paid off today. You have to be brave to make that decision in that moment because you know bringing in a player in the game is a risk," said Bompastor.
"We had a good conversation with Veerle and she was clear on why she wasn't starting the game. That clarity was important for when she came in.
"She had a really good performance against a top player. Sometimes when it doesn't work, it's not so positive, but today it was.
"You have to react and be the one that analyses the situation and make decisions. I'm used to it, even if you don't see lots of substitutions in the first half most of the time in football."
