Duncan Keith had a goal and three assists, and the Blackhawks used a four-goal third period to finish off the St. Louis Blues with a 5-1 victory in Game 6 of their first-round playoff series on Sunday.The Hawks won four in a row after a slow start in St. Louis. The defending Stanley Cup champions will play the winner of the Minnesota-Colorado series in the Western Conference semifinals. The Avalanche lead the Wild 3-2 heading into Game 6 in Minnesota on Monday night.Jonathan Toews, Patrick Sharp, Andrew Shaw and Keith scored in the third period as the Blackhawks improved to 14-2 in home playoff games over the last two seasons. Corey Crawford made 35 saves, keeping his team in a tie game when St. Louis controlled the second period.T.J. Oshie scored for the Blues, who outshot the Blackhawks 36-27. Ryan Miller finished with 22 saves.St. Louis went 0 for 6 in 10 minutes of power-play time over the first two periods, wasting a chance to take the lead. The Blues went 2 for 29 with the man advantage for the series.The Blackhawks also struggled on the power play, but they scored when it mattered most.With Jay Bouwmeester in the box for tripping, Keith made a nice stop to keep the puck in the St. Louis zone, then fired a pass over to Toews. The captain beat Miller over his right shoulder for a 2-1 lead just 44 seconds into the third period.It was Toews’ third goal of the series. He also scored on a breakaway in overtime of Friday night’s 3-2 win.Toews’ 23rd career postseason goal seemed to take the air out of the Blues, and it got even worse for St. Louis. Sharp got loose for a breakaway, shook off a stick to the face by defenseman Kevin Shattenkirk and slid a shot past Miller.Sharp’s first point of the playoffs sent a charge through the towel-waving sellout crowd of 22,144, and there were mocking chants of “Mil-ler! Mil-ler!” as Shaw added his second goal of the series and helped set up Keith for his second.It was an eerily similar playoff exit for St. Louis to a year ago, when the Blues also were eliminated by the defending Stanley Cup champions in six games in the first round. In that 2013 playoff series, St. Louis won the first two games at home against Los Angeles, then lost four in a row.This year was supposed to be different, especially after the Blues acquired Miller from Buffalo on March 1. But they lost their last six games of the regular season, putting them in a first-round series against their rivals, the Hawks.St. Louis rebounded for two 4-3 overtime victories, but the Blackhawks found their stride when the series shifted to Chicago. Crawford had a shutout in Game 3, Patrick Kane scored in overtime in Game 4, and Toews’ breakaway score in St. Louis put the Blackhawks in position to advance.Brent Seabrook returned from a three-game suspension. Seabrook was punished by the NHL for his wipeout hit on Blues captain David Backes in Game 2.Backes exacted a measure of revenge when he delivered a hard hit on Seabrook into the end boards in the second period. But Seabrook added two more assists and had six points for the series.Bryan Bickell redirected Seabrook’s high slap shot past Miller for a 1-0 lead 4:12 into the game. Alexander Steen skated behind the net before finding Oshie in front for the tying score.The Blues outshot the Blackhawks 17-3 in the second, but couldn’t beat Crawford. St. Louis had one shot trickle across the goalmouth, keeping it tied at 1.

NOTES—Kris Versteeg was scratched after he played in the first five games. F Joakim Nordstrom was active for the first time. … Keith tied a playoff career high with four points.