It started with some verbal sparring in news conferences. Then it became physical with a touchline flare-up when they last crossed paths.
What's in store next in the increasingly spiky relationship between Jose Mourinho and Arsene Wenger?
The game between Arsenal and Chelsea at Emirates Stadium on Sunday pits the top two teams in the English Premier League together. Some of the world's best players are on show, and the league title is at stake.
Yet, much of the build-up has focused on the animosity between the coaches, who have developed the biggest managerial rivalry in the league.
Wenger and Mourinho have sought to play down their feuding this week, preferring to focus on the game itself. But when the pressure ramps up, and the atmosphere gets more intense on Sunday, don't be surprised if there is an exchange.
"He is a manager of a big club in the same city where I work and I live," Mourinho said on Friday. "A big club with the same objectives we have in the competitions we play and, because of that, always comes a little bit of rivalry.
"But for me, it's no different from when I was at Inter with the (AC) Milan manager, is not different from when I was at Real (Madrid) with Atletico managers, or at Porto with Benfica managers. It's the same."
Yet, Mourinho undeniably has targeted Wenger.
In the past, Mourinho has called the Frenchman a "voyeur" who "speaks, speaks, speaks about Chelsea." He has criticized the lack of English players in Wenger's teams, and took things even further last season when he labeled Wenger a "specialist in failure" because Arsenal had gone without a trophy from 2005-2014.
Wenger, for his part, called Mourinho "disconnected with reality and disrespectful" in 2005, during the Portuguese coach's first spell at Chelsea. When Arsenal played Chelsea at Stamford Bridge in October, Wenger was incensed by a challenge on Alexis Sanchez and walked across the Chelsea technical area to complain. Mourinho gestured for Wenger to retreat, only for the Arsenal manager to push Mourinho in the chest, triggering a telling-off for both men from the fourth official.
At the heart of Wenger's frustration is likely his inability to get the better of Mourinho. In 12 meetings, Mourinho has never lost to Wenger.
"We have not always lost, first of all, in 12 attempts. We have come close to beating them a few times and they've always had very strong teams," Wenger said on Thursday.
"I'm not a great believer in history. I just think football is down to the fact that the performance on the day will decide the game and the result, so let's focus on that."
Tactically, Mourinho has had the edge over Wenger, as he has with the rest of the Premier League's top managers. In 29 games against Arsenal and the two Manchester clubs in his two spells with Chelsea, Mourinho's teams have lost only twice.
While Wenger's teams have adopted an easy-on-the-eye passing game, Mourinho's sides can be more pragmatic and negative -- but more successful at the same time.
Indeed, another of Wenger's criticisms of Mourinho, back in 2005, revolved around playing styles.
"Once a sport encourages teams who refuse to take the initiative," Wenger said, referring to Mourinho's Chelsea, "the sport is in danger."
Another sub-plot to Sunday's game is Chelsea midfielder Cesc Fabregas, who left Arsenal for Barcelona in 2011 after eight years and more than 300 appearances. Arsenal reportedly opted out of its buy-back option when it became apparent he could leave the Nou Camp, and Mourinho moved to sign the Spain international.
It will be the first time Fabregas has played against Arsenal in the Premier League.
"I know why he chose Chelsea. I don't know why he didn't choose Arsenal," Mourinho said.
"I just know that we promised him we'd build a team very adapted to his style of play. That he was going to be an important player in our project. And that, normally, good projects always end with titles. He was looking for that."