CHICAGO -- The story of the Stanley Cup finals continues to be the power of one.

For the fourth straight game, one goal separated the winner from the loser, as the Chicago Blackhawks defeated the Tampa Bay Lightning 2-1 in Game 4, tying the best-of-seven series at 2-2.

It's a rarity: only the third finals in NHL history (others were 1951 and 1968) to have each of the first four games be decided by one goal.

Chicago left winger Brandon Saad's goal at 6:22 of the third period broke a 1-1 tie and proved to be the difference.

"Saad's been great," Chicago coach Joel Quenneville said. "I loved his game tonight. Great power move to the net (for the winning goal). He's big, fast and dangerous. A very good performance."

Game 5 will be in Tampa, while Game 6 is Monday in Chicago.

"We played our best game, but we still have to get to another level," Chicago defenseman Duncan Keith said. "We have to be patient and not get frustrated. We have to have our best game of the year in Game 5."

Despite his team being on the losing end, Lightning coach Jon Cooper praised it.

"I know the series is tied 2-2, but we've had a chance every single game," Cooper said. "You can't ask for much more from your team. ... (Chicago) got one more break than we did."

Chicago goalie Corey Crawford stopped 24 of Tampa Bay's 25 shots, while 20-year-old rookie Andrei Vasilevskiy stopped 17 of Chicago's 19 shots.

"If you told me (Vasilevskiy) was going to come in and give up just two goals, that's a (heck) of a job in my book," Cooper said. "That kid gave us every chance to win the hockey game. We just scored one goal. I thought he was great."

Vasilevskiy was a late replacement for Tampa Bay's No. 1 goalie, Ben Bishop, who was scratched due to lingering injuries.

"It doesn't matter who we put in there, we have full confidence in both guys," Cooper said. "He proved he can play in the pinnacle of the sport. That's a pretty big thing for a 20-year-old guy."

Added Lightning defenseman Jason Garrison, "(Vasilevskiy) was our best player out there tonight. He played extremely well, didn't look nervous at all."

Quenneville drew a chorus of laughs from the media after the game when asked about Tampa Bay's goalie situation.

"We expected their goalie in the net, but also expected the other goalie in the net, so I guess it was 50-50 tonight," Quenneville quipped.

Cooper wouldn't say if Bishop will play in Game 5, but promised "Bish is going to play again in this series. I just don't know which one."

Saad scored the game-winner with a great second effort. He grabbed the puck along the boards, cut cross-ice, fired a 15-foot wrist shot that was deflected by Vasilevskiy, picked up his own rebound and backhanded it through Vasilevskiy's legs.

Tampa Bay threw a flurry of shots at Crawford in the final 90 seconds, including two point-blank attempts, but he turned back everything sent his way. Crawford also had luck on his side as one shot sailed over his shoulder and bounced off the crossbar.

After a scoreless first period, Chicago and Tampa Bay traded goals in the second period.

Chicago broke the scoreless tie when team captain and center Jonathan Toews tipped in a shot by left winger Patrick Sharp at 6:40 of the second period. Toews' first goal of the series and 10th of the playoffs came shortly after Sharp hit the post behind Vasilevskiy on a partial breakaway.

But Tampa Bay came right back, tying the game at 11:47 on a wrist shot by winger Alex Killorn. After a scramble in the Chicago end, the puck was passed to the front by center Valtteri Filppula to Killorn, who roofed his ninth of the playoffs past Crawford.

"We've seen in this series, when we've had the lead briefly, they've always seemed to bounce back," Toews said of the Lightning. "We did a better job at