Smith, relegated to a backup role behind Dwayne Roloson, made 31 saves for his first shutout in more than a year, and Vincent Lecavalier scored a power-play goal in the first period before leaving with an injury in the Lightning's 2-0 win on Sunday night.
Nate Thompson added an empty-net goal with 22 seconds left to seal Tampa Bay's fifth straight victory. The Lightning improved to 99 points, one behind fourth-place Pittsburgh in the Eastern Conference.
"I felt very patient," said Smith, who made his fourth start since Dec. 18. "I saw a lot of pucks.
"Every win is rewarding. But against the defending Stanley Cup champions, whenever you beat a team like that, it's more rewarding."
Smith started because Tampa Bay was playing the second of back-to-back games.
The 29-year-old goalie played in 42 games last season, and 41 during the 2008-09 season for the Lightning. This season, he was out because of a knee injury from Dec. 20-Jan. 20 and never reclaimed his role after Roloson was acquired from the New York Islanders on New Year's Day.
"You've got a backup that fills in and gives you a chance to win in back-to-back games," Lightning coach Guy Boucher said. "That's two back-to-backs he's gone in for and done a good job. We can't ask for better."
Smith was tested heavily in the final 30 minutes, but held off the Blackhawks and earned his 11th NHL shutout. In addition to 31 shots that reached Smith, Chicago fired 21 that were blocked in front of him.
The Blackhawks are clinging to eighth place in the West with 92 points and are still trying to secure a playoff spot with four games left.
Chicago is one point ahead of ninth-place Calgary and three ahead of 10th-place Dallas.
"We need more, especially being down," Chicago coach Joel Quenneville said. "We're certainly looking for more.
"We didn't get enough traffic on [Smith]. Giving up the first goal was something that was important, especially the way they love to trap and stay back and just flip it out and play that type of game."
Lecavalier was accidentally high-sticked by Chicago's Michael Frolik early in the second period and didn't return. He needed three stitches to close a cut over his left eye and, according to Boucher, had trouble seeing.
"Vinnie wanted to come back, but there was a lot of blood," Boucher said. "He couldn't see, so I think there's a scratch. Hopefully it's just a minor scratch in the eye."
The team said Lecavalier would be reassessed on Monday.
Simon Gagne had two assists to extend his point streak to six games. He has four goals and seven assists in the span.
Chicago rookie Corey Crawford made his 24th straight start and stopped 13 shots.
Lecavalier's power-play goal at 7:56 of the first was the only score in the period.
Seconds after winning a faceoff in the Chicago zone, Lecavalier drove to the edge of the net, past defenseman Brent Seabrook, and directed in St. Louis' perfect feed from the right corner.
Lecavalier was clipped by Frolik's stick at 4:42 of the second period as Frolik drove to the net. Lecavalier paused for a minute to shake off the impact, but then skated off the ice without help and went directly to the dressing room.
After killing off a double-minor penalty to Frolik, the Blackhawks began dominating and outshot Tampa Bay 11-4 in the period.
Smith blocked several tough chances as the period progressed. Among his best stops were a point-blank pad save on Frolik, a body save on Viktor Stalberg's deflection, and a pad save on Tomas Kopecky's drive.
"I thought we had pretty good control of the entire game, just have to get more bodies out there and find a way to get one past him," Stalberg said.
During a Chicago power play early in the third, Smith stopped Kopecky's drive from the right circle and a rebound by Troy Brouwer.
Smith made a point-blank stop on Marian Hossa with 40 seconds left after the Blackhawks pulled Crawford for an extra skater.
Lightning D Eric Brewer sat out with an undisclosed lower body injury. LW Ryan Malone was a healthy scratch. ... RW Patrick Sharp, Chicago's leading goal scorer with 34, missed his sixth game because of an injured left knee. ... Blackhawks C Dave Bolland sat out his 10th due to a concussion.