Arsenal were denied from making it four wins from four in the Europa League group stages after Vitoria forward Bruno Duarte scored in second-half stoppage time to rescue a 1-1 draw on Wednesday.
The visitors looked dangerous down the flanks with their new-look formation featuring three at the back, but it was Vitoria who had came closest to breaking the deadlock on two occasions during the early exchanges.
Rodrigues Pepe broke for the hosts before unleashing a shot from 25 yards which beat Emiliano Martinez in the Arsenal goal, only to bounce back off the post in the eighth minute.
Martinez was then forced into action when Lucas Evangelista fired in another effort from the edge of the area which the goalkeeper did well to palm wide.
Vitoria continued to hit Arsenal on the counter and forced Martinez into another save in the 19th minute, this time from a set-piece.
Edmond Tapsoba was left unmarked as he rose highest to an Evangelista free-kick but was denied by the Argentinian goalkeeper.
Stand-in captain Rob Holding headed over Arsenal’s first real effort at goal before Davidson curled narrowly wide for the hosts.
There was a moment of concern when Dani Ceballos was forced nine minutes after the restart with a hamstring problem and was replaced by Matteo Guendouzi.
Both sides struggled to created chances, with Shkodran Mustafi‘s header over the crossbar proving to be the only effort of note heading into the final 15 minutes of the match.
Arsenal finally made the breakthrough which the game so badly needed with nine minutes remaining.
Nicolas Pepe curled in an inviting cross from a set-piece which found Germany international unmarked from six yards from goal to head home.
Arsenal were left off when Wolves loan striker Leo Bonatini blazed over the crossbar after great build-up play.
However, Vitoria scored a stoppage-time equaliser through Bruno Duarte after the visitors failed to clear a right-wing cross.
Vitoria nearly snatched victory as Mustafi deflected a cross onto his own post before Rochinha fired a speculative volley narrowly wide, but the Gunners held onto a point in Portugal.