"I'm in tonight," Karlsson told the assembled media in Washington after the Senators' morning skate. "I'm feeling good lately, and I think it's about time to play some hockey again.
"I've been away for a while. All the other guys are up to pace. For me, it's about trying to find the feeling that I had before and just get the pace in me. Just trying to be focused and trying to play well."
Karlsson recorded a shot less than a minute into Thursday's game.
The NHL's top defenseman last season, Karlsson sustained a serious injury to his Achilles tendon Feb. 13 when Pittsburgh's Matt Cooke stepped on the back of his leg.
Karlsson was expected to miss the rest of the season following surgery but recently returned to practice and was back with regular defense partner Marc Methot for Wednesday's skate.
The Senators need two points in the standings to clinch a playoff spot.
Information from The Associated Press was used in this report.