Tierney took over the reins of the University of Denver men's lacrosse program in July 2009 after serving as the head coach at Princeton since the 1988 season. In his nine seasons at DU, Tierney has amassed an impressive 122-36 overall record and an even more impressive 48-4 conference mark.

The Pioneers have reached Championship Weekend five times in the last eight seasons, including the 2015 National Champion Pioneers, the first program to sit atop the national plateau from a state not sharing a boarder with the shores of the Atlantic Ocean.

Sitting at 4-2 through its first six games, Denver ended the 2015 campaign on a 13-game winning streak to win the title. The Pioneers not only entered the 2016 campaign with a 13-game winning-streak, but a 16-game winning streak at Peter Barton Lacrosse Stadium, the longest such active streak in the nation at the time.

For the second-consecutive season, the Pioneers finished BIG EAST play perfect, this time with a 5-0 record in the conference before sweeping the BIG EAST Tournament in Villanova. Tierney coached his first Tewaaraton finalist in 2015 in Wesley Berg, who was named to the NCAA All-Tournament Team and broke Denver's career points and goals records on April 11 against St. John's.

Denver began its national title defense on a seven-game winning streak to run its overall streak dating back to 2015 to 20 games, the eighth longest streak in NCAA history. The streak was the longest for Tierney since leading the Tigers to 29-straight from March, 1996- March, 1998. Denver's opening run included wins at [9/10] North Carolina, at [2/1] Notre Dame and a neutral site win against [3/3] Duke. After dropping its first contest in more than a year to Penn State, Denver stayed perfect in its three seasons in BIG EAST play, going 5-0 in its regular season schedule.