Downing's second-minute header preceded a stunning hat-trick by Luis Suarez at the DW Stadium as the Reds racked up 12 goals in their last three fixtures.
But Reina was required to make reflex saves from Emmerson Boyce and Franco Di Santo before the three points were secured - a fact not lost on the 'keeper's teammates.
Downing told the Liverpool Echo: "As we won comfortably in the end, some people won't see how important Pepe was against Wigan but as players we appreciate it.
"Sometimes it can be hard for a 'keeper. Outfield players make many mistakes in games but they don't lead to anything.
"If a 'keeper makes a mistake generally it ends up in the back of the net. It's a tough position to play.
"That save at 2-0 was really important. At 2-1 it would have been a different game. But Pepe kept it out and we pushed on, got the third goal and then it was easy for us. He's a top class 'keeper."
Suarez stole all of the headlines, of course, after his treble established the Uruguayan as the top scorer in the Barclays Premier League.
The Reds' No.7 now has 21 goals in the league - and Downing expects that number to pass the 30 mark before the campaign concludes.
"Luis is on fire at the minute," the 28-year-old added.
"He's scoring all different types of goals and if you have a striker like that you've always got a chance of winning games.
"To get 21 goals in 27 games in this league is frightening. We've still got 10 games to play so he could easily get 30-odd goals.
"He must have a big chance for the Player of the Year awards."
With just league football to focus on during the remainder of the season, Brendan Rodgers' side will now begin preparation for a huge clash with Tottenham this Sunday.
Confidence is high after the victory at Wigan, according to Downing, who insisted Liverpool can triumph again when Gareth Bale and co visit Anfield.
"We played some great football and on a tricky pitch dominated long periods of the game," Downing said of Saturday's win.
"The early goal helped settle us down. It had been a long time since I scored a header - probably going back to my days at Aston Villa.
"It was nice to get a goal and the manager has been telling me to get in those kind of positions to score. It was a great ball from Coutinho and he caused them lots of problems. He's had two really good games for us.
"The Premier League is different from the leagues he has been in before but he has settled really well. Hopefully he keeps playing like that.
"It think it's coming together. We've got 10 games to go and we've got to keep winning games.
"There's no point saying we want to finish fourth, fifth or sixth. Anything could happen if teams slip up.
"We need to keep chipping away and focus on Spurs. They have some good offensive players but we played them off the park at White Hart Lane earlier in the season and how we lost I just don't know.
"The way we're playing at the moment I'm confident we can get a win."