Substitute Nicolas Pepe rescued Arsenal with two sublime free-kicks in the last 10 minutes of their Europa League group game against Vitoria Guimaraes at Emirates Stadium.
Arsenal were losing 2-1 when Pepe came on in the 75th minute and he scored five minutes later with a curling effort from 25 yards.
He repeated the feat in stoppage time as Arsenal avoided their second straight defeat and retained their place at the top of Group F.
Former Tottenham youngster Marcus Edwards had earlier cut inside and fired into the bottom corners to give Vitoria a shock lead, before Arsenal's Brazilian teenager Gabriel Martinelli nodded in his fifth goal in just his third start to make it 1-1.
Bruno Duarte restored the visitors' lead on 36 minutes, pouncing on a rebound to send Arsenal into the half-time break a goal behind.
The Gunners, who were poor for large patches of the game, burst into life in the final 10 minutes as Martinelli was denied from close range before Rob Holding's header was well held by the goalkeeper.
Arsenal manager Unai Emery made 10 changes from the side that lost to Sheffield United in the Premier League on Monday but was forced to bring on Matteo Guendouzi and Dani Ceballos at half-time, before Pepe made the difference.
Full results of Wednesday matches
Arsenal 3-2 Guimaraes
Celtic 2-1 Lazio
Dynamo Kyiv 1-1 FC Copenhagen
Eintracht Frankfurt 2-1 St Liege
Getafe 0-1 Basel
Malmo FF 2-1 Lugano
PSV 0-0 LASK Linz
Rennes 0-1 CFR Cluj
Sevilla 3-0 Dudelange
Sporting 1-0 Rosenberg
Trabzonspor 0-2 Krasnodar
Roma 1-1 Borussia Monchengladbach
AZ Alkmaar 6-0 FC Astana
Basaksehir 1-0 Wolfsberger
Besiktas 1-2 Braga
CSKA Moscow 0-1 Ferencvaros
Porto 1-1 Rangers
Gent 2-2 Wolfsburg
Ludogorets 0-1 Espanyol
Partizan 0-1 Manchester United
Qarabag 2-2 APOEL
Slovan Bratislava 1-2 Wolves
Young Boys 2-0 Feyenoord
St-Etienne 1-1 Oleksandriya
Young Boys 2-0 Feyenoord
Source: bbc