LONDON—For nearly a decade, Arsenal made its annual trip across North London to the home of rival Tottenham Hotspur and returned without a victory. There were galling close calls and embarrassing capitulations. Nearly all of them involved some kind of pratfall. 

So when the streak ended on Sunday afternoon with a 2-0 win for Arsenal at the Tottenham Stadium, the result could have stood as a milestone on its own. But as the players celebrated in front of the small contingent of traveling fans, they understood that they had claimed something far more surprising. By the time Arsenal left its hated rival’s home, it was a genuine contender in the Premier League title race.

As the season approaches the halfway point, Arsenal holds an eight-point lead over Manchester City, which has won championships in four of the past five seasons. For Arsenal, the youngest squad in the league with an average age of 24.1, this is uncharted territory.

“I saw a team with a lot of courage, determination, quality, and they really wanted it today,” Arsenal manager Mikel Arteta said. “They are young and they are starting to believe and have experience.”

The tests for Arsenal will now come in quick succession. By March, the club could either be in charge of the race or practically out of it. First there is a difficult home game against a newly drama-free Manchester United on Jan. 22, and then a potentially season-defining clash against Manchester City on Feb. 15. But as intimidating as that schedule may be, Arsenal goes into it in a better position than most of its fans can remember. In fact, after 18 of 38 games, the club has never had this many points since the Premier League began in 1992.

What makes it so stunning isn’t Arsenal’s record in itself—the team’s controlled performance on Sunday underlined again that it is clearly one of the smoothest, most efficient teams in English soccer today. The shock comes from the sheer speed of Arsenal’s turnaround. The club is 15 points better off than it was at this stage last season and 23 ahead of its total at this point in 2020-21.

Much of that comes down to the faith the club has placed in Arteta. Only hired in December 2019, when Arsenal was in free fall, he currently has the fifth-longest active tenure in the Premier League—all the more impressive considering he had never managed before. During that spell, there were plenty of moments when his inexperience was obvious. Had Arsenal not committed so completely to a rebuilding project, might have seen Arteta fired. The fans weren’t shy about calling for his head then, but they have happily changed their tune since. At the final whistle on Sunday, Arsenal supporters were marking their first victory at Tottenham in nine years with a song about “Super Mik Arteta” on loop.

“In the last few years there were places we haven’t won for 15, 17 or 20 years,” Arteta said. “I would like to do it all at once.”

Not only has Arteta been given more time to prove himself than most managers, he’s also enjoyed a free hand in building the squad he needed. That meant investing in young talent quickly to suit his playing style—seven of Sunday’s starters weren’t playing for Arsenal when Arteta arrived in London—and drumming out the aging, highly-paid stars who didn’t. (The club had no qualms about cutting loose two of the highest earners in its history, Mesut Ozil and Pierre-Emerick Aubameyang, after Arteta decided he preferred not to work with them.)

All of which has left Arteta exactly with the team he designed. All it needed, in this era of Manchester City reeling off championships with near-immaculate seasons, was an opening.

That seemed to arrive on Sunday when City lost its own crosstown derby against Manchester United, 2-1, on Saturday. Though City had been ahead with 15 minutes to go, an uncharacteristic wobble combined with a confusing offside decision by the officials, saw the defending champions allow two goals in quick succession and lose for the third time this season. 

In recent years, Arsenal might have seen a chance like that and choked. Instead, the team wasted no time in stamping its authority on the Tottenham game.

The first break in the game came in the 14th minute, when Bukayo Saka fired a hard cross straight at Tottenham goalkeeper Hugo Lloris, only for Lloris to break the first rule of goalkeeping and push the ball into his own net. The stadium fell into near silence as 61,000 people wrapped their heads around what they had just witnessed. It didn’t last long as the Arsenal fans took a beat and burst into celebration. 

Arsenal’s Martin Odegaard scores the Gunners’ second goal against Tottenham on Sunday.

Photo: DYLAN MARTINEZ/REUTERS

Twenty-two minutes later, Arsenal added a second goal when Martin Odegaard fired into the bottom corner of the goal from 25 yards out. The Norwegian playmaker who was supposed to be a wunderkind at 15 is finally a star at 24 and at the heart of the Arsenal offensive machine.

“Especially in the first half, I thought he was incredible,” Arteta said. “He’s really showing a different kind of presence, the way he’s influencing the game.”

He’s also influencing the standings. Right now, Arsenal is on pace to finish the season with 99 points. That number is so ridiculous that only two teams have ever managed it. And to be clear, it’s highly unlikely Arsenal will become the third. But Arteta knows that if his team is going to win a first Premier League title in 19 years, it will have to be close.

“I don’t want to do too much calculation,” Arteta said. “It will demand almost perfection.”

Write to Joshua Robinson at Joshua.Robinson@wsj.com