TAMPA, Fla. -- Freshman Luke Mittelstadt scored two third-period goals in two-and-a-half minutes, and top-ranked Minnesota beat Boston University 6-2 on Thursday night in the opening game of the NCAA Frozen Four.

Mittelstadt gave Minnesota a 3-2 lead on a power play with 18:20 left in the third period, and his second came from the same spot at the left circle for his fifth goal of the season -- and third in the NCAA tournament.

Logan Cooley added two empty-net goals to reach 22 on the season.

The five-time national champion Gophers (29-9-1) seek their first title since 2003 against Quinnipiac on Saturday. Minnesota has outscored its opponents 19-5 in the NCAA Tournament.

Minnesota took a 2-1 lead late in the first period on back-to-back goals in 50 seconds by Mike Koster and Rhett Pitlick. Koster scored his sixth goal of the year on a blast from the circle. Pitlick finished a between-the-legs pass from Aaron Huglen.

Minnesota appeared to take a 3-1 lead with 44.5 seconds to go in the second period on Cooley's rebound, but it was taken away after a challenge for goaltender interference.

Boston University (29-11-0) had its nine-game winning streak, dating to Feb. 24, snapped. The Terriers were seeking their first national title since 2009.

BU entered unbeaten at 21-0-0 when scoring the game's first goal. And the Terriers led 1-0 when Sam Stevens sent in a rebound for his eighth goal of the season. BU tied it at 2-all on Jay O'Brien's deflection in front of the net for the lone goal of the second period.

It was the fifth meeting between the two programs in the national semifinals and first since 1995.