Geekie extended the Lightning lead to 2-0 at 16:30 with a one-timer from the right circle that beat Lindgren to the stick side off a pass from Hagel.
"I think maybe we came out flat on Thursday, but that game was past us and we couldn't let it happen again," Geekie said. "Every guy stepped up. I could go down the whole roster. I think everyone was great tonight."
Sourdif made it 2-1 at 7:04 of the second period after Jakob Chychrun sent the puck toward the net from the point and Sourdif redirected the puck past Vasilevskiy from the slot.
"It's definitely good for the confidence, but two points would've been better," Sourdif said. "I thought we didn't come out very strong. It's tough on a back-to-back, but it's their home opener and we knew they were going to come out strong. I've got to be better prepared and come out for a full 60 minutes against a hockey team like that."
Guentzel added an empty-net goal at 17:55 off a pass from Nikita Kucherov for the 3-1 final. John Carlson, playing in his first game against his former team, also had an assist on the goal.
"Just the first put us behind the 8-ball and it ends up costing us," Capitals coach Spencer Carbery said. "The second and third were fine. I thought we did some good things in those 40 minutes. Just the first period cost us."
NOTES: Carlson was plus-1 in 20:35. … Lightning forward Nikita Kucherov had an assist and moved into a tie with Joe Nieuwendyk and Mike Bossy for 67th all-time with 1,126 points. … Vasilevskiy and Washington’s Dylan Strome each played in his 600th NHL game. … Capitals defenseman Matt Roy left the game with a lower-body injury.