Manchester City issued a statement of intent by knocking out Arsenal 1-0 in the FA Cup on Friday.
Nathan Ake's 64th-minute goal settled the fourth-round match at Etihad Stadium and the result may yet reverberate through the rest of the season.
Arsenal leads City by five points at the top of the English Premier League, but its seven-game unbeaten run was ended by City, which has three straight wins in all competitions.
England's two best teams have a league showdown at Emirates Stadium on Feb. 15. For now, City manager Pep Guardiola has gained an edge on his former assistant, Arsenal boss Mikel Arteta.
"I know how difficult it is to beat Arsenal. They lost one game in the Premier League, so I know how difficult it is," Guardiola said.
Defender Ake was the unlikely match-winner after curling a low shot past goalkeeper Matt Turner.
Arsenal had chances while enjoying the better of the first half. Takehiro Tomiyasu and Leandro Trossard forced saves from City goalkeeper Stefan Ortega, and Eddie Nketiah fired narrowly wide from close range.
The visitors were made to pay when City improved after the break and Ake produced the decisive strike.
"(I'm) really disappointed," Arteta said. "We could have got much more out of the game. In the big moments in big matches you have to make the difference."
While a place in the fifth round of the cup was at stake, it was impossible to ignore the wider context of a match between the teams who are the front-runners in the league race.
Arsenal has been in outstanding form, picking up 50 points after 19 games and playing with a confidence not seen since Arsene Wenger's title-winning teams of the late 1990s and early 2000s.
As if to underline the fact that the cup is neither team's priority, Guardiola and Arteta left key players out of their lineups.
Guardiola benched Ederson, Kyle Walker, Joao Cancelo and Bernardo Silva.
Arteta left out Aaron Ramsdale, Ben White, William Saliba, Martin Odegaard, Gabriel Martinelli and Oleksandr Zinchenko.
Arsenal's new signing, Trossard, was given his first start since joining from Brighton last week.
Despite the changes, Arsenal created the better chances in the first half but could not make them count.
City began to control the game after the break without creating many clear-cut openings until Ake broke the deadlock.
Substitute Alvarez's strike from outside the box beat Turner, but came back off the post. Jack Grealish picked up the rebound and laid off to Ake, who hit a first-time effort low into the corner.
Elimination gives Arsenal one less distraction in its bid for the title and Arteta hopes to strengthen his squad before the transfer window closes at the end of the month.
The London club has been linked with a $74 million move for Brighton midfielder Moisés Caicedo, but Arteta would not answer specific questions about the player.
"We have been pretty active in the market. We have some necessities," he said. "If something else is available, the club is willing to try to do it when it is reasonable and hopefully he's a player that can improve our squad."