Hagelin immediately clicked with his new team, with the Penguins fully utilizing his straight-ahead speed. After having initial success playing left wing next to center Evgeni Malkin, Hagelin and right wing Phil Kessel joined center Nick Bonino in mid-March, when Malkin sustained an upper-body injury.
Malkin missed the final 15 regular-season games, but with Hagelin, Kessel and Bonino the Penguins thrived. Hagelin had six goals and seven assists, helping the Penguins win 13 of those 15 games.
Hagelin and Kessel improved with Bonino, who adapted to their north-south style. Pittsburgh seemed to embrace the speed generated from its new second line, which led Penguins coach Mike Sullivan to slot rookie left wing Conor Sheary into the top line alongside Sidney Crosby, in place of veteran forward Chris Kunitz.
When Malkin returned in Game 2 of Pittsburgh's Eastern Conference First Round series against the New York Rangers, Sullivan decided to keep his former linemates with Bonino. That proved to be the right call.
Hagelin scored once in five games against New York, but surged early against the Washington Capitals in the Eastern Conference Second Round. He scored one goal in each of the series' first two games before having his most impressive playoff performance in Pittsburgh's series-deciding 4-3 overtime win in Game 6, when he had a goal and two assists.
The speed of Hagelin's line has proven difficult for larger teams to defend and could be a key factor again against the Lightning; Tampa Bay defensemen Brayden Coburn, Victor Hedman and Andrej Sustr range from 6-foot-5 to 6-foot-7 and each weight at least 220 pounds. Coburn, Hedman and Sustr are split across Tampa Bay's three defense pairings, meaning Hagelin will always be out against one of them.
After the Rangers surrendered five goals in three of five games against the Penguins, New York defenseman Marc Staal marveled at Pittsburgh's tempo.