Jarry has won his last four decisions, including a sloppy 7-6 home win against New Jersey last week, in which he allowed six third-period goals. He rebounded two nights later against the Devils and has earned a point in 11 of his last 12 starts.
Guentzel scored his 21st at 4:03 of the third period to help the Penguins win their fourth straight.
Bryan Rust and Brian Dumoulin made a plays at the blueline and along the wall to keep the puck in the zone and get it to Sidney Crosby near the goal-line. Crosby set up Guentzel, who ripped a high slap shot past Jeremy Swayman's glove from the left faceoff dot.
Pittsburgh has 14 wins and points in 16 of its last 19 games overall. The Penguins have 12 wins and points in 13 of their last 16 home games against Boston, dating to March 11, 2012.
Swayman stopped 28 shots for the Bruins. They lost their second straight following a season-long six-game win streak. The Bruins have nine wins in their last 14 games.
Swayman, the top college goaltender last season for Maine, has allowed more than two goals only once in his first seven NHL starts. In his past three appearances, Swayman has stopped 82 of 84 shots, including a shutout. Swayman is the fourth Boston goaltender the Penguins faced this season.
Pittsburgh and Boston are battling for two of the top four spots in a tightly-contested East Division.
The Penguins have a two-game series against the Washington Capitals after Tuesday's home game against the Bruins, as Pittsburgh's next three game are against teams jockeying for top-four positioning in the standings.
Two of Boston's final nine games — including Tuesday at Pittsburgh — are against teams currently holding a playoff spot. Four of Boston's final nine are against the New Jersey Devils or Buffalo Sabres, the two bottom teams in the East Division, while the other three are at home against the fifth-place New York Rangers.
The Penguins and Bruins played a 0-0 game through two periods.
Both teams had 10 shots in the first period, but Pittsburgh outshot Boston, 11-8, in the second, as the Penguins started to gain control in the later stages of the period. Boston blocked 10 shots, while the Penguins had six blocks and neither team went on the power play in the first two periods.
Guentzel and Rust nearly tucked a puck inside the post off the rush for Pittsburgh in the second, while Jarry denied a quality Craig Smith one-timer in the final minute of the period.
CROSBY SECOND AGAINST THE B'S
Crosby passed Jaromir Jagr for the second-most points all-time by a Penguins' player against Boston.
Crosby now has 16 goals and 64 points in 49 games against the Bruins, trailing only Mario Lemieux, who finished with 73 points against Boston. No active player in the NHL has more points against Boston than Crosby, who has five goals and 24 points in his last 19 games against the Bruins.
On Saturday, in a win against New Jersey, Crosby joined Wayne Gretzky as the only players in NHL history to register a point-per-game season in each of their first 16 years in the league. He also passed Lemieux and Evgeni Malkin for the most 20-plus goal seasons in franchise history.