It perhaps wasn't so shocking that the side capable of halting Arsenal's championship push would be captained by Granit Xhaka, an ex-Gunner. Replacement striker Brian Brobbey scored an stoppage-time leveling goal after second-half strikes from Saka and Trossard had put the visitors ahead following a early goal from Sunderland skipper Ballard.
Proved to be a rocky night for the Premier League leaders, but Arsenal maintain a seven-point lead over City, who are at home Liverpool on Sunday, and the hosts, though the Blues could reduce the gap to six in Saturday's evening fixture.
The Swiss international – who departed the Emirates Stadium in last year seeking what he described as a fresh opportunity – has been exceptional in the promoted side's midfield this season after signing from Bayer Leverkusen, but the 33-year-old's form on Sunderland's home turf will not have surprised Arsenal fans. The Swiss international revived his Gunners stint under Mikel Arteta, who did not want to lose him.
The Black Cats entered the match with nothing to lose after making the best start to a top-flight season by a promoted side over 10 games since Hull in the 2008-09 season. A deflected strike from the midfielder against the Toffees on Monday night had lifted them up to fourth place, a position not many home supporters would have envisaged before a ball was kicked given that their team had spent eight years away from the Premier League.
Xhaka's expertise, much of it earned during his lengthy spell at the Emirates, and captaincy have assisted the team quickly adjust to Premier League soccer. He appeared to thrive in the physicality of the contest.
Arteta, once more without Jesus, Martin Ødegaard, Havertz, Madueke, Viktor Gyökeres and Martinelli, had an early concern when Mikel Merino, playing up front after scoring two goals in Tuesday night's 3-0 European win at Prague, was caught by an arm from Ballard as he attacked a ball into the Sunderland area. Merino was fit to continue.
Eze almost took advantage of an error from Enzo Le Fée, who was dispossessed on the border of the penalty area, but the shot flew over the bar.
Isidor fired off target at the opposite side before a further lengthy stoppage after a head collision between the midfielder and Timber, who had to continue with a bandaged head.
A tougher setback was to follow for stunned Arsenal. The home team launched a free-kick into the visiting area and Ballard held off Declan Rice to lash the shot past David Raya after it was knocked out. It was the opening strike Arsenal had let in since their last visit to the North East in September's end, when they had underlined their title credentials with a late win over the Magpies.
Arsenal had kept a club-record eight successive clean sheets in all competitions since Nick Woltemade's goal against them at St James' Park.
The Black Cats ensured that it was a further difficult outing to the area for Arsenal, who found themselves under pressure for periods after the break.
They needed a moment of class, and it arrived in the 54th minute. The midfielder took the ball off his opponent and a flowing move featuring the winger and the striker ended with the forward beating Roefs at his near post.
The visitors pushed for a next score and the coach made three changes to his offense – he sent on the substitute, Chemsdine Talbi and Adingra – midway through the second half.
A further example of skill was not long in coming. Arsenal worked the ball from one flank to the other, and the Belgian, on the edge of the area, found enough room to lash a right-foot shot into the top corner.
Raya had to be alert in the last 10 minutes as the hosts pressed for a equalizer, but could not stop an spectacular finish from the substitute after the ball was headed into the box. The strike was met by a huge roar.
Appropriately the defender – like Xhaka another ex-Gunner, this one coming through Arsenal's academy – had the final say with a diving block at the feet of the attacker in the match's final moment.
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