Whether it was waking up from the New Year's Eve hangover or Mikel Arteta's half-time break, Arsenal had changed gears.
The ball stagnations, the lack of rhythm and, in the case of David Raya, the bad mistakes of the first half had been solved.
It was a set piece (Arsenal's tenth goal in the league this season through this ploy) and Ethan Nwaneri were the main architects of a victory that puts the north London club on the right foot for 2025.
Trailing leaders Liverpool by nine points before the match, who still have a game in hand, the Gunners could not afford to drop any more points here.
Doing so would have come close to handing Arne Slot's men the title as a belated Christmas present. Arsenal are far from perfect and will need to improve as the season progresses if they are serious about usurping the Reds before the end of the season.
But there were promising takeaways, such as Nwaneri's rise to the task at hand. In his first Premier League start, he was involved in both of Arsenal's goals in the second half.
Bryan Mbeumo scored his ninth home goal with a good shot from the right
Gabriel Jesús found the net in consecutive games for the Gunners for the first time since 2023
Arsenal took the lead with a goal from Mikel Merino after another set piece
His corner kick in the 50th minute was rejected by goalkeeper Mark Flekken, who wasted it. Gabriel Jesús hit the ball, which Sepp Van Den Berg deflected towards Mikel Merino, who scored.
Just four minutes later, Nwaneri jumped in and sent a cross into the box. Nathan Collins headed the ball to Gabriel Martinelli and scored.
They were the actions of a 17-year-old who, after watching his academy mate Myles Lewis-Skelly rise to prominence in his three recent consecutive starts in the league, is eager to make his own mark.
Nwaneri became the youngest player in the Premier League, aged 15 years and 181 days, against Brentford on September 18, 2022. This was his first start in the league, more than two years later. Some wait.
Bukayo Saka's injury has left a big void on the right wing that someone must try to fill. This was Nwaneri's big audition for the lead role and while there is still more to come from him, he has certainly gotten ahead of himself.
More generally, Raya, who is arguably the best goalkeeper in the league, put in a performance that you will know was far from his usual standards.
Martin Odegaard's errant pass that Christian Norgaard intercepted. The Bees captain stepped up to free Bryan Mbeumo, diving from the right with Riccardo Calafiori in front of him.
The Italian retreated aimlessly, allowing Mbeumo a goal in sight. He surreptitiously dragged the ball inside Raya's near post with a left-footed shot on the edge of the area.
Gabriel Martinelli scored a confidence-boosting goal that sent traveling fans wild
Arteta's team selection for the north London club's first match in 2025 took everyone by surprise
Raya's position should have been better. But everything was going to get worse for him. Keane Lewis-Potter's shot, straight at the Spaniard, slipped through the goalkeeper's hands.
Time seemed to have stopped when Raya sprinted towards his goal line to perform a spectacular diving claw move to snatch the ball off the line.
It was a poor mistake redeemed by the spectacular. Luckily for him, those mistakes would not cost him dearly: Gabriel Jesús scored in the first half to level the game before the break.
This was Raya's first game against his former employers (he was unable to face Brentford last season as he was on loan from the club) and the home fans reveled in his misfortune.
Arteta's team selection for the north London club's first match in 2025 took everyone by surprise.
Kai Havertz was not in the squad due to illness, Declan Rice started on the bench due to fitness issues and teenager Lewis-Skelly was replaced by Riccardo Calafiori.
Havertz's absence, supposedly due to illness, was a hard blow for the Gunners. It is a key source of your goals.
Arsenal started cheerfully, locking the rival in their own half. Jesús enjoyed much of the ball in the first 10 minutes, passing the ball to both sides of the area.
In his first Premier League start, Ethan Nwaneri was involved in both of Arsenal's goals in the second half.
This was David Raya's first game against his former team and the home fans reveled in his misfortune in the first half.
The Bees agreed to give up possession, feeling there would be opportunities on the counterattack. That proved true: Mbeumo was released by Damsgaard to give Brentford a goal lead in the 13th minute.
That lead almost doubled shortly before the half hour mark. Shot from Keane Lewis-Potter, straight at Raya, which the Spaniard wasted before that last shot on the line.
The Gunners finally began to get going and got back into the match through, in effect, a human game of pinball. The ball bounced back anyway before Thomas Partey fired past goalkeeper Mark Flekken.
He spilled the ball and Jesús finished with a diving header.
That fueled Arsenal's rejuvenation thanks to those two goals in the eight minutes after the break.
Martinelli grew into the game, advancing with enthusiasm, as the visitors thrived on the early gaps their healthy lead allowed them.
In the end, everything was simple for the visitors. But Arteta will know his team can take advantage of this until 2025.