Third periods have not been kind to the San Jose Sharks all season, an unfortunate trend that’s only been exasperated in the last few weeks and on this road trip.

Thursday, the Sharks allowed third-period goals to John Ludvig and Rickard Rakell before Bryan Rust added an empty-netter in a 6-3 loss to the Pittsburgh Penguins at PPG Paints Arena.

Fabian Zetterlund, Marc-Edouard Vlasic, and Klim Kostin all scored for San Jose, with Kostin’s goal, off an assist from Mikael Granlund, tying the game 3-3 with 1:18 left in the second period.

But Ludvig scored at the 2:38 mark of the third period, and Rakell’s goal, a deflection off a shot by Pierre-Olivier Joseph, came two minutes later. Rust’s empty netter put the game away with 1:56 to go.

The Penguins (29-27-9) outshot the Sharks 13-4 over the final 20 minutes.

Goalie Magnus Chrona stopped 25 of 30 shots for the Sharks (16-42-7), who also gave up a third-period goal in Tuesday’s 3-2 loss to the Philadelphia Flyers.

On a streak that’s now seen them lose 11 of their last 12 games, the Sharks have been outscored 19-6 in the third period. For the season, San Jose has scored 49 goals and allowed 93 in the third.

“I thought we really battled hard,” Sharks coach David Quinn said. “It’s fortunate that we weren’t able to defend a little bit better around our net in those instances in the third period. Maybe it was fatigue.”

The Sharks had a scary moment in the second period as Granlund had to be assisted off the ice after he suffered what appeared to be a right leg injury.

Granlund had the puck on his stick to the right of the Sharks’ net when he was checked against the boards by Rust. As the two fell after the check, Granlund’s leg got caught under Rust, and he remained on the ice in obvious discomfort as the play left the zone.

Granlund left the ice with the help of head athletic trainer Ray Tufts, and fellow forward Luke Kunin with 7:10 left in the second period. But he was back on the Sharks’ bench shortly afterward and returned to the ice with 3:38 left in the second.

Granlund also assisted on Vlasic’s first-period goal and now has a team-leading 33 assists and 42 points on the season.

“Those are always scary situations,” Granlund said. “Don’t want to get into it too much, but you kind of feel like, ‘Oh boy.’ But I was able to play the rest of the game.”

Vlasic and Zetterlund both scored in the first period as the Sharks took a 2-1 lead.

After Henry Thrun kept the puck in the Penguins’ zone, he fired it across the ice to Calen Addison, whose shot on net was stopped by goalie Tristan Jarry, Zetterlund, though, was left open in front of the net, and easily knocked in the rebound to tie the game 1-1 at the 14:31 mark.

Just 4:30 later, after Kostin’s shot on net was blocked, Vlasic picked up the loose puck, skated below the goal line, and put a shot toward the front of the Pittsburgh net. The puck went off Jarry, then Penguins forward Marcus Pettersson before it bounced into the Pittsburgh net with 59 seconds left in the period.

The Sharks played with five defensemen, as Jan Rutta (lower body) remained out for the third straight game and Jacob MacDonald came down with an illness and was determined to be unavailable roughly 90 minutes before the start of the game.

“I don’t know if it changed anything,” said Sharks defenseman Mario Ferraro, who had 27:05 in ice time, “besides making sure we managed ourselves and took short shifts.”