After leading Czech Extraliga goaltenders with a 2.16 goals-against average in the 2012 playoffs, Mazanec was selected by the Nashville Predators in the sixth round (No. 179) of the NHL Draft that year.

In 2012-13 he ranked fourth in playoff goals-against average (2.13) and tied for second in shutouts (two) to help HC Plzen win the 2012-13 Extraliga title. He stopped 48 shots in Game 7 of the final, a victory in double overtime.

Mazanec split the 2013-14 season between Nashville and Milwaukee of the American Hockey League, playing 25 NHL games and the fifth-most minutes (1,369:32) of any rookie goalie in the League. He made his NHL debut on Nov. 12, 2013 against the New York Islanders, stopping 30 shots. Mazanec earned his first NHL win Nov. 16, 2013, making 39 saves against the Chicago Blackhawks, the most by a Predators goalie in any game that season.

On Nov. 19, 2013, against the Detroit Red Wings he became the youngest goalie Predators history to get a shutout, stopping 27 shots. He got his second shutout four games later on Nov. 27 against the Columbus Blue Jackets, making 19 saves. Mazanec was named the NHL's Rookie of the Month for November 2013 after going 5-4-1 with two shutouts, a 2.00 goals-against average and a .933 save percentage.

Mazanec was named AHL Player of the Week for April 7-13, 2014, after going 3-0-0 with a 1.00 GAA and a .964 save percentage. He appeared in two games for the Predators in 2014-15 and had a 2.26 GAA and .915 save percentage.

Mazanec, who led HC Plzen to a championship in the Czech under-18 league in 2007-08, represented the Czech Republic at the 2009 World Under-18 Championship and the 2011 World Junior Championship.

NOTES & TRANSACTIONS

• Signed as a free agent by NY Rangers, December 6, 2017.
• Traded to Vancouver by NY Rangers for Vancouver's 7th-round pick in 2020 NHL Draft, February 12, 2019.
• Traded to Tampa Bay by Vancouver with Vancouver's 3rd-round pick in 2019 NHL Draft and a conditonal 1st-round pick in 2020 NHL Draft for J.T. Miller, June 22, 2019.