Olivier Giroud put the Gunners in front just before the half-hour mark, before the hosts hit back with two goals in the space of five minutes before half time.
Santi Cazorla then missed a late penalty as Arsène Wenger’s side slipped to their first Premier League defeat in seven games.
“The penalty, it can happen and Santi falling… there is nothing you can do,” Flamini told Arsenal Player. “We tried and tried and tried until the last minute but we can’t give any excuses – today we lost the three points.
“It’s a shame because we started the game well, we went 1-0 up and then after they scored [twice] before half time it became more difficult for us.
“We tried to push on in the second half, we had some opportunities but of course it is disappointing because we didn’t get any points.
“Sometimes it happens and now it is important to recover and focus on the next game.”
Goalkeeper, Petr Cech believes Arsenal were the better team but it was just one of those days for them.
“I think we don’t want to take credit from West Brom but across the 90 minutes we were the better side. We had chances and a lot of opportunities and we were unlucky as we scored an own goal. Apart of that, we were on top of them and looked like the side that was going to win the game, even in the second half.
“I thought when we had the penalty that we would still have a chance to search for the third goal but it was one of those games where it was not going our way. But I like our reaction and although everything went against us a bit, we kept going until the last minute and were still creating opportunities. We have to regroup and continue working,” he said.