BOSTON — Brady Tkachuk scored 21 seconds into overtime for the Ottawa Senators in a 3-2 win against the Boston Bruins at TD Garden on Saturday.

Bruins forward Elias Lindholm had a shot stopped by Senators goalie Linus Ullmark, which led to a 2-on-1 rush the other way for Ottawa, which Tkachuk finished off.

Tkachuk also had an assist, and Josh Norris and Michael Amadio scored. Ullmark made 14 saves for Ottawa (7-7-0), which has won three of its past six (3-3-0).

It was Ullmark’s first time facing Boston after spending three seasons there from 2021-24. The Bruins traded Ullmark to Ottawa on June 24 in exchange for goalie Joonas Korpisalo, forward Mark Kastelic and a first-round pick in the 2024 NHL Draft, which they used to select Dean Letourneau (No. 25).

Pavel Zacha and Brad Marchand scored, and Jeremy Swayman made 31 saves for Boston (7-7-2), which has lost two of its past three (1-1-1).

Norris gave the Senators a 1-0 lead with 7.8 seconds left in the first period, sneaking a one-timer under the crossbar on the power play.

Zacha tied it 1-1 at 4:51 of the second period with a spinning backhand shot after Nikita Zadorov kept the puck alive in the offensive zone.

Marchand gave the Bruins a 2-1 lead 15 seconds later, elevating a cross-crease feed from Justin Brazeau.

Amadio tied it 2-2 at 17:16 of the second, skating in and snapping a shot past Swayman from behind the right circle.

Senators defenseman Travis Hamonic exited at 4:11 of the third period after taking a shot off his arm.

Ottawa outshot Boston 12-0 in the third period.