Arsenal came away from the Diego Armando Maradona Stadium with a precious three points, beating hosts Napoli 1-0 in the opening round of the Champions League league phase on Wednesday.
Martin Odegaard settled it in the 75th minute. Tzolis slipped the ball to the captain near the edge of Napoli's box, and Odegaard let it run across his body before lashing a left-footed strike off the left post and into the net.
The win lifts Arsenal to three points and 12th in the standings, ahead of their rivals on goal difference. Napoli sit 30th, still without a point.
Arsenal bossed the first half. They fired off 13 shots, a new club record for the first half of an away match in the Champions League, according to The Sun.
Mikel Arteta's side took the game to their opponents while Allegri's men dropped deep and looked to hit on the break.
Saka flashed some skill in Arsenal's first real opening, though his overhead kick caused no real problem. His cross then found Eze, who nodded it back to Merino, and the Spaniard wasted a golden chance to break the deadlock with a header from close range.
Napoli had their moments through Politano and De Bruyne, but neither seriously tested Raya.
Just before the break, Odegaard released Saka, who surged forward powerfully only to blaze his shot over the bar.
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The second half followed a similar pattern, though the play crept closer to both goals with Arsenal still holding a clear edge.
Odegaard's strike stiffened the visitors' belief, and they pushed for a second while Napoli laboured in vain for an equaliser.
Tzolis lashed a fierce effort in stoppage time that rebounded to Havertz, who bundled it home, but the flag went up for offside. The Gunners held on for a precious 1-0 win.