The Reds hopes of making the last 16 of the competition were dealt a major blow when Brazilian forward Hulk and Sergei Semak struck within minutes of each other to leave the Anfield outfit a large deficit to overcome in a week's time.
The loss comes in the aftermath of Monday's league defeat to West Brom, and Gerrard is now looking toward the weekend game against high-flying Swansea as a chance to right recent wrongs.
"We're obviously down. On the back of two defeats, it's a difficult moment but we need a reaction," Gerrard told the club's official website. "We've got a big game in a couple of days against Swansea, and we need to bounce back.
"Up until the 70th minute against Zenit, the game was under control. It was a tough night in tough conditions. We're disappointed with the two sloppy goals we conceded, but the tie is not over. If anyone can pull it back, it's us."
Liverpool has been involved in many European comebacks over the years - most famously against AC Milan in the 2005 Champions League final - and Gerrard hopes the fans will play a major part when Zenit travels to Anfield for the second leg.
"We'll have an advantage with our supporters," Gerrard said. "If they can create the noise they're capable of, get behind the team and we can get an early goal, it's game on.
"But we are disappointed. It wasn't the result we wanted - we wanted an away goal and to try and sneak away with a clean sheet, but if you concede sloppy goal, you get punished and that's what happened."