Zenit coach Andre Villas-Boas has questioned the awarding of a penalty that gave Sevilla a two-goal buffer in their UEFA Europa League tie.
Villas-Boas' men were denied at least extra-time in their quarter-final tie with the defending champions, after Kevin Gameiro's late goal handed Sevilla a 4-3 aggregate win.
Bacca's conversion put Sevilla 3-1 up in the tie.
"For the penalty it is not clear. I spoke with the referee and he was positive about awarding it," Villas-Boas said.
"His location is difficult. But checking the replay I think it is not clear. For me it seems more contact from the striker with our defender than the other way."
"Regarding our performance in the second half I think we deserved at least to reach extra time, even to score a third goal with the [Jose] Rondon and Hulk chances," the Portuguese boss said.
"The most difficult thing for us was having four key players out for the first game in Seville," he said.
"When you face an opponent like Sevilla, it is important to have as many players available as you can. The same today with [Ezequiel] Garay.
"The four players who could not play there today were important.
"The game lasts 90 minutes and the team usually does not behave the same way during the whole match.
"For instance Sevilla played very well in the first half, but then in second they were non-existent.
"Obviously I'd like to be performing at high levels during 90 minutes, but it is not possible. There are emotions, there is an opponent and anything can happen. There are no perfect 90 minute performances."
