"It's do or die for us every game," the defenseman said after scoring his 10th of the season with 1:01 to go for a 2-1 victory over the Columbus Blue Jackets on Monday night. "We're not out of it yet.
"We're going to keep fighting every game, win every game we can."
Andy McDonald had a goal and an assist, David Perron set up both goals and Chris Mason made 27 saves for St. Louis, which has won a season-high five straight at home. The Blues are four points behind Colorado with three games to go for the final Western Conference playoff spot and need to finish ahead of the Avalanche, who swept them in the regular season.
They're also two points behind Calgary, which has three games to go.
"There's not a lot of room for error here," McDonald said. "We've played extremely well, I think, the last couple months and we've got to keep going. Obviously, we need some help."
Colorado has four games to go and can knock out the Blues on Tuesday night with a victory at Vancouver.
"You want to kind of have your fate in your own hands," Johnson said. "But we're in this position and we'll have to see what other teams do."
Derick Brassard scored an early power-play goal and Mathieu Garon made 32 saves for the Blue Jackets, who have lost three straight and were shorthanded. Leading scorer Rick Nash (upper body) was scratched after participating in the morning skate and center Andrew Murray was sidelined by a blow to the head when Keith Tkachuk elbowed him into the boards late in the first period.
Tkachuk drew a double minor on the play and he was sidelined after two periods with a lower-body injury. Coach Claude Noel said Murray had a head injury and was surprised Tkachuk wasn't penalized further.
"I thought we played with a tremendous amount of courage, as short as we were," Noel said.
A holding call on Marc Methot with 1:43 to go in overtime opened the door for the Blues, and Johnson scored his 10th of the season on a slap shot from the point.
Garon said he was screened by two players on the game-winner.
"I knew he went to my blocker side, but I couldn't see it," Garon said. "I couldn't find the puck at all."
St. Louis avoided elimination by taking the game to overtime. The Blues have been the NHL's worst at home most of the season with the late-season surge raising their record to 17-18-5.
McDonald scored his 23rd goal and second in three games on a break off a Perron feed to tie it midway through the second period.
The Blues hardly appeared in desperation mode in the first period, going nearly 13 minutes before finally registering a shot. Columbus outshot St. Louis 11-4 and took the lead on Brassard's power-play deflection at 3:10.
"Plenty of concern based on the way the game was going," Blues coach Davis Payne said. "We had to make sure we understood just exactly how hard a fight it was going to take."
Tkachuk played in his 1,200th game. ... Blues F Patrik Berglund (upper body) also missed the third. ... Paid attendance of 17,601 was about 1,500 shy of capacity, ending a string of 15 straight sellouts for the Blues.