PITTSBURGH -- The Pittsburgh Penguins hired Mike Johnston in the summer of 2014 and tasked him with guiding the star-laden roster back to the NHL's elite.

The marriage lasted all of 18 months.

The Penguins fired Johnston and assistant Gary Agnew on Saturday morning with the high-profile team languishing in the middle of the pack in the crowded Metropolitan Division. Johnston went 58-37-15 during his brief stint with Pittsburgh.

Mike Sullivan, who was head coach of the Boston Bruins from 2003-06 and was serving as the coach of the Penguins' affiliate in the American Hockey League, replaces Johnston. Sullivan will run his first practice with the Penguins on Sunday. Pittsburgh hosts Washington on Monday night.

Pittsburgh fell to Los Angeles in a shootout on Friday to drop to 15-10-3 and in fifth place in the Metropolitan. Perhaps even more troubling than the uneven performances has been an inability to find the net. The Penguins rank 28th in scoring.

"We're not far from the top of the division, but we're not far from the bottom either," general manager Jim Rutherford said Saturday. "It's never a comfortable time. It's bothered me, but I felt it was necessary."

The Penguins hope Sullivan's arrival gives the team a needed spark. Sullivan went 70-56-15 in two years with the Boston Bruins and spent most of the past decade bouncing around as an assistant coach. He spent the 2014-15 season as player development coach for the Stanley Cup champion Chicago Blackhawks.

Pittsburgh will retain assistant coach Rick Tocchet. Jacques Martin, who had been serving as a special assistant to Johnston, will move down to the bench alongside Sullivan.

Sullivan had the Wilkes-Barre/Scranton Penguins of the AHL off to an 18-5-0 start and Rutherford believes Sullivan's newness with the organization can pay immediate dividends.

"I wanted somebody new to come in that the players aren't going to totally know," Rutherford said. "(I think) that he can come in and mould what we're doing going forward."

Rutherford brought in Johnston on June 25, 2014, after the Penguins cleaned house by letting general manager Ray Shero and coach Dan Bylsma go following a second-round playoff collapse against the New York Rangers.

Johnston promised to bring in a system that focused on puck possession, one designed to allow former MVPs Sidney Crosby and Evgeni Malkin to spend plenty of time in the offensive zone.

Following a blistering 16-4 start in 2014-15, the Penguins struggled with injuries and an ineffective power play that seemed more concerned with setting up pretty goals rather than producing shots or traffic around the net. Pittsburgh exited quietly in the opening round of the playoffs against the Rangers.

Rutherford gave the roster an overhaul over the summer, acquiring forward Phil Kessel to give Malkin a potent running mate and bringing in veteran forward Eric Fehr while bolstering the bottom six, moves that were expected to take some of the burden off their top lines.

Yet the Penguins failed to develop anything resembling momentum this season. Crosby has just 19 points and is on pace for the worst season of his decade-long career and the power play continued to languish near the bottom of the league despite an abundance of playmakers. Pittsburgh is 26th with the man advantage this season.

"It's not easy to score goals in this league but certainly our power play should be a lot better, which should win more games for us," Rutherford said.

Kessel has all of nine goals with more than a quarter of the season gone. Only the play of Malkin -- whose 13 goals and 13 assists lead the club -- and goaltender Marc-Andre Fleury have kept Pittsburgh from a complete collapse.

While Rutherford maintains the Penguins "for the most part" respected Johnston, Rutherford became concerned following listless losses to Columbus and New Jersey on consecutive nights in the middle of November. Though Pittsburgh played better in the aftermath, the results were not consistent enough for Johnston to keep his job.

"I look at this snapshot over the first 27 games and I felt that we've underachieved," Rutherford said.

The previous time Pittsburgh replaced a coach in the middle of the season, Bylsma led the franchise to its third Stanley Cup in 2009.

"I believe he's the guy that can come in and really take control and really make some guys more accountable when we're not performing that way we should be," Rutherford said