Saracens director of rugby Mark McCall has said he struggled to find any positives in the 20-15 defeat by Wasps.
Wasps secured victory at Twickenham on Saturday as Saracens became the ninth defending champions in 11 years to lose on the Premiership's opening day.
"I thought we scrummaged well and put them under pressure at scrum time," McCall said afterwards.
"We were a little bit more physical in the second half, but there are very few positives to take out of that."
The champions failed to record a try against their London rivals at Twickenham, but McCall remained more concerned with his side's defending.
Tom Varndell's ability to allude two Saracens attempts at tackles when landing the winning score highlighted their problems.
"Sometimes [not scoring a try] can happen, but I thought the number one problem was defensively," McCall added.
"Sometimes you can get a lot of tries from defence.
"We pride ourselves on our defence and in the first half we slipped off a lot of tackles, they made a lot of yards.
"It's unusual for us and unlike us and something we're going to have to address in the week.
"We've got off to a bad start this season, but we'll work hard during the week and hopefully produce a much better performance next week against Bath."