BILBAO, Spain : Arsenal began their Champions League campaign with a 2-0 win away to Athletic Bilbao on Tuesday, with Gabriel Martinelli making an immediate impact from the bench to open the scoring and another substitute, Leandro Trossard, netting the second.

Mikel Arteta's side, beaten at the semi-final stage last season by eventual winners Paris St Germain, were the better team on the night, but laboured to put away Athletic who were backed by a boisterous San Mames stadium, until the substitutes arrived.

Martinelli replaced Eberechi Eze in the 71st minute, with Arsenal struggling to find a breakthrough despite creating plenty of chances, and the substitute netted an impressive solo goal after less than a minute on the pitch.

The Brazilian forward was sent racing through on goal after a flicked pass from Trossard, and the two combined again three minutes from time, with Martinelli's pullback from the byline finished off by Trossard.

The game took a while to get going before Arsenal ventured forward and began to create chances. Athletic defender Andoni Gorosabel made a crucial clearance with Eze about to pull the trigger from close range after a Noni Madueke pass.

Viktor Gyokeres had a couple of opportunities - a strike which never troubled Athletic keeper Unai Simon and a diving header which went wide, with Arsenal looking to the Swedish striker's movement and strength to break through Athletic's backline.

Arsenal began to turn the screw and increase the pressure in the early stages of the second half, while Athletic always posed a threat on the counter but the game was failing to match the frenzied atmosphere in the stands.

Mikel Arteta sent Trossard on for Gyokeres, but it wasn't until the introduction of Martinelli that Arsenal really got going.

Trossard's ball from inside his own half sent Martinelli through and, after controlling it neatly, he drove forward into the area and kept his nerve to send a low shot past Simon.

Martinelli then turned provider, going past his marker before finding Trossard, who had time to take a touch before getting a shot away, which took a deflection on its way past the keeper.

Arsenal began last season's campaign with a 0-0 draw at Atalanta, and they almost had to settle for a similar result, but Arteta turned to his bench to defeat an Athletic side making their first Champions League appearance since 2014.

Arsenal host Olympiakos in their next Champions League game on October 1 with Athletic away to Borussia Dortmund on the same day.

Subs Martinelli and Trossard earn Arsenal 2-0 win at Bilbao