CHICAGO -- The Chicago Blackhawks loosened up one of the tightest series in recent Stanley Cup Playoff history with a dominating third period Sunday.

The Blackhawks scored early, then again, and again and again to run roughshod over the St. Louis Blues in what turned out to be the final 20 minutes of a best-of-7 Western Conference First Round series that was aptly termed a battle by players and coaches on each side.

Chicago made sure the series didn't go the distance with a 5-1 win in Game 6 at United Center.

After losing the first two games at Scottrade Center in overtime, the Blackhawks won four straight to move one step closer to becoming the first team to repeat as Stanley Cup champions since the 1997-98 Detroit Red Wings.

How did the Blackhawks get it done against St. Louis? Here are five reasons:

1. Experience pays off

Blackhawks coach Joel Quenneville used the word "brutal" several times to describe the overtime losses in Games 1 and 2. It was a fair description of them, but his players never sulked or panicked or even seemed worried in the least bit.

When St. Louis took a lead in the third period of Game 4 and had a real chance to take a 3-1 lead in the series, the Blackhawks ratcheted up their game, scored the tying goal and then the winner in overtime.

And when it was time to turn on the jets, to show the Blues what champions are made of, the Blackhawks did just that in the third period of Game 6 on Sunday, scoring four goals to deliver a knockout blow for the ages.

Playoff experience played a big role in Chicago's first-round series victory. The Blues lost their composure at times and it cost them when they made mistakes that led to goals. The Blackhawks always kept their composure, and it might be the main reason they're moving on.

"We've been there," Blackhawks forward Andrew Shaw said. "We've had our backs against the wall in previous series. Going down 2-0, it's tough to come back from. The boys came together, leadership took over, and we just stayed positive and kept doing the little things right. We found ways to win."

2. Stars being stars

The Blackhawks know things are good in a playoff series when their top four scores are Jonathan Toews and Duncan Keith with seven points, and Patrick Kane and Brent Seabrook right behind them with six. Seabrook even missed three games because of his suspension.

Chicago's star players stepped up at the time when star players are supposed to step up.

Toews' three goals were all game-winners, including his overtime breakaway goal in Game 5. Kane scored three goals, including the overtime winner in Game 4. Keith had four points in Game 6, including the primary assist on Toews' winner.

Patrick Sharp was quiet all series, but he finally stepped up in a big moment, scoring a breakaway goal in the third period Sunday to give Chicago a 3-1 lead. Blues coach Ken Hitchcock repeatedly called Sharp's goal "a backbreaker" three times in his postgame press conference.

Marian Hossa didn't have a big series on the score sheet, but his goal in Game 5 gave the Blackhawks a 1-0 lead.

"Every time someone seemed to be scoring a goal he had a 19, or 88, or 81 or a 10 on his back," Hitchcock said, referring to Toews, Kane, Hossa and Sharp. "That's all I really know."

3. Crawford wins goaltending battle

Blackhawks goalie Corey Crawford said after Game 2, a 4-3 overtime loss at Scottrade Center, that he needed to be better if Chicago was going to come back from a 2-0 series deficit.

He absolutely was.

Crawford arguably stole Game 3 with a 34-save shutout in a 2-0 victory. He then allowed six goals over the remaining three games to finish the series with a .935 save percentage and 1.98 goals-against average.

By comparison, Blues goalie Ryan Miller faced 30 fewer shots than Crawford did in the series (215-185), but had a .897 save percentage and 2.70 GAA.

Crawford made the big saves when the Blackhawks needed him to. Instead of losing his confidence after giving up late third-period goals in Games 1 and 2 before losing in overtime, Crawford challenged himself and got better.

"That's what a leader does, he's not afraid to take the blame and take the criticism and the negative attention, and he pulls through," Blackhawks captain Jonathan Toews said. "Your teammates respond to play and behavior like that. Pretty amazing job by him."

4. Bickell plays big, again

Blackhawks left wing Bryan Bickell earned a four-year, $16 million contract for his play in the playoffs last season, when he surprised even his own teammates and himself with 17 points, including the game-tying goal with 76 seconds left in Game 6 of the Stanley Cup Final.

He had a difficult regular season as injuries and a crisis in confidence plagued him, but against the Blues, Bickell once again showed why the Blackhawks signed him to a big money deal in the offseason.

The Blues were supposed to have the physical edge in the series, but Bickell helped negate that by wreaking havoc with his big body, deceptive speed and his impressive skill.

He started the series on the third line, and finished on the top line with Toews and Hossa. Bickell had the game-tying goal with 3:52 left in the third period of Game 4, and the first goal early in Game 6. He added an assist in Game 5 to give him three points in the series.

Bickell was also credited with a team-high 35 hits (19 more than anyone), and he was third on the team with 19 shots on goal.

"I needed to bring my physicality to help my linemates and cause turnovers," Bickell said. "It gives me confidence. It's playoff time and I love it."

5. PK domination

The Blues were supposed to have the advantage on special teams heading into the series. They had a better power play and penalty kill than Chicago in the regular season.

However, the Blackhawks wiped out the Blues' perceived advantage by knocking their power play out cold. St. Louis went 2-for-29 in the series, including 0-for-6 in Game 6.

Not only did the Blues fail to score on the power play, the Blackhawks generated momentum off the penalty kills.

Blackhawks players got in shooting lanes, blocked shots, and rarely gave up an inside opportunity. The fans at United Center took to chanting "Zeus" for Michal Handzus, who was arguably Chicago's best penalty killer as the lead shot blocker up top.

The Blues didn't help their cause by consistently looking to shoot from the point or the half-wall without even bothering to attempt an inside play from below the goal line, but Chicago's PK was a big factor in that. It didn't give up much free space at all.

"We've kind of caught fire here over the last part of the season," Keith of the penalty kill. "The last three-quarters to half of the season we've been pretty solid on it. We know it's going to have to be good."

Follow Dan Rosen on Twitter: @drosennhl