The Impact hold a two-goal buffer heading into Tuesday's return semi-final leg after Ignacio Patti and Victor Cabrera inspired the Canadians to a 2-0 victory at Stade Olympique in Montreal on March 18.
Only one other MLS franchise - Real Salt Lake in 2010-11 - have made an appearance in the Champions League final but no team from Canada have progressed so deep into the tournament.
"We have some guys that are fast. But at the end of the day, [Alajuelense] are the team that has to come out and push the game to score," said Klopas, who has acquired John Smits on loan from FC Edmonton to provide backup for goalkeeper Evan Bush for the second leg.
"We can keep the game at 0-0, and we go through. We have to manage the game. We know they're going to come out hard. They're playing at home, with their atmosphere.
"We just have to be mentally ready and be prepared for a fast start for them."
"I think that it's good that the league was able to move the game," Klopas said.
"It would be hard, because some of the injuries we have right now, playing in the two tournaments, it's not that easy.
"It's good. We can really prepare, get some guys the extra rest they need to make sure they're really ready and sharp to go."
The iconic Estadio Azteca is the location for Wednesday's second leg.
