The Washington captain passed Brett Hull with his latest hat trick, his 34th in the NHL.
Ivan Miroshnichenko scored twice and Anthony Beauvillier and Rasmus Sandin each had a goal and an assist for the Capitals (36-28-9), who have won three of their past five games. Logan Thompson made 36 saves.
Dylan Guenther scored twice, and Clayton Keller and Mikhail Sergachev each had three assists for the Mammoth (37-30-6), who went 1-3-0 on their four-game homestand. Vitek Vanecek made 17 saves. Karel Vejmelka entered the game in relief at 9:54 of the third period and made one save.
Miroshnichenko scored at 2:07 of the first period on a slap shot past the blocker side of Vanecek to give the Capitals a 1-0 lead.
Guenther scored a power-play goal at 13:04, beating Thompson with a one-timer on the glove side off a pass from Keller to tie the game at 1-1.
Guenther scored his second goal at 16:59, sliding the puck between the legs of Thompson off a pass from Keller to give the Mammoth a 2-1 lead.
Logan Cooley scored a power play goal at 19:53, tapping in a loose puck that was behind Thompson off a shot from Sergachev to make it 3-1.
Ovechkin scored at 5:01 of the second period, tapping in a shot by Rasmus Sandin to cut the lead to 3-2.
Ovechkin scored his second goal at 11:28, sending a wrist shot from the point past Vanecek to tie the game 3-3.
Beauvillier scored a power-play goal at 2:43, tipping in a shot from Cole Hutson to give the Capitals a 4-3 lead.
Sandin scored at 6:02, firing the puck on net from the point while Vanecek was out of position to extend the lead to 5-3.
MacKenzie Weegar scored at 8:06, throwing a wrist shot from the point past Thompson to make it 5-4.
Miroshnichenko scored his second goal at 9:54, flicking a backhanded shot through the legs of Vanecek to push the lead back to 6-4.
Ovechkin scored an empty-net goal at 19:54 for the 7-4 final.
