(REUTERS) - Arsenal defender Per Mertesacker rued his side's "massive loss" to West Ham on Sunday but was confident the Gunners will bounce back from the setback in their Premier League opener.

The Germany international bemoaned his side's lack of decisiveness in front of goal as Arsenal were well beaten by a West Ham side that defended strongly and looked to hit their London rivals on the break.

"It's a massive loss for us," Mertesacker was quoted as saying on the club's website (www.arsenal.com) about the 2-0 scoreline.

"Overall, we weren't decisive enough, especially in the final third. It looked like the last ball was always the wrong decision."

Arsenal failed to win four of their opening six games last season and the 30-year-old centre-back believes Arsenal could not afford another upset in their next game, when they visit Crystal Palace on Sunday.

"Sometimes it's good to come back from a massive loss. I think we are capable of coming back," he said. "It's very important. We want to have a better start than last season so we need to be very cautious of the situation.

"To start with a game like that is not good but to bounce back is even more important now."