After Borussia Dortmund's fans opened their doors to Monaco rivals stranded by a bomb attack that postponed their match, the visitors returned the solidarity gesture Wednesday decked out in the German squad's black and yellow, AFP reports.

All day Monaco fans piled into the German club's boutique, snapping up Dortmund gear before kick-off.

"We've sold hundreds of scarves and jerseys since this morning, and it's almost only the French who've been buying," said Sultan Karakas, who was manning the boutique's till.

Monaco may have won 3-2 in the end -- much to the annoyance of Dortmund coach Thomas Tuchel, who said his shaken players should have had more time to process the attack -- but the visiting team's fans had already won their hosts' hearts earlier in the day.

Social media lit up with photos of Monaco and Dortmund supporters sharing beers and snacks in a display of camaraderie rarely seen between rival teams.

Police ramped up security around Signal Iduna Park -- likewise for the Bayern Munich fixture against Real Madrid in Munich -- but the boosted police presence appeared to reassure match-goers.