There are no second chances for Wellens' men going into Saturday evening's elimination play-off against Hull KR after they finished outside Super League's top four for the first time in nine years.
There were even times during the height of their injury crisis that Saints looked in danger of missing out on the play-offs altogether, but Wellens says they will enter the business end of the season in confident mood after winning six of their last seven matches.
"The big key for us was obviously getting players back fit and getting players in key positions playing regularly," Wellens said.
"Once we did that, I think it's no coincidence our performances have improved. It shows throughout the competition that teams struggle when they're missing key players and we're not alone in that.
"We finished fifth in the table but, if you look at our last seven or eight games, it's probably the form of a top-two side and that gives us huge confidence going into the play-offs."
Hull KR, back in the play-offs after missing out in 2012, will also go to Langtree Park full of confidence after beating St Helens three times already this year.
Wellens needs no reminding that the Robins completed a league double and knocked his side out of the Challenge Cup at the first hurdle.
"It will be a tough game because they've obviously beaten us three times this year," he said.
"Their coach has done a fantastic job. They, like us, have probably been hit by injuries, but certainly on their day they can be a match for anybody, as they showed the other week when they won at Leeds."
While Saints have welcomed the comeback of their latest casualty, England hooker James Roby, the Robins are buoyed by the return of no fewer than nine players who sat out last week's home defeat by London.
They include skipper Michael Dobson and key forwards Cory Paterson and Mickey Paea, who will all be hoping to extend their Hull KR careers by at least one more week.
"Obviously I know it's going to be my last game if we lose but that's not what's really driving me," said Dobson, who is returning to the NRL with Newcastle Knights in 2014.
"Obviously I'd like to be at Old Trafford for the club and for the boys that have worked so hard this year. We've got a long road and it starts at St Helens on Saturday.
"It's a knockout competition now and we've got to show up on Saturday. If we play to the best of our ability, anything can happen."