Dmitry Kulikov scored a power-play goal 10:46 into the third period to lift the Panthers to a 2-1 victory over Ottawa on Sunday night.
Anderson was 9-0-1 in his last 10 starts against his former team and Ottawa had won 11 of its 12 previous meetings with Florida overall, and six of seven on the road.
Kulikov's wrist shot from top of the left circle beat Anderson while Sergei Gonchar was serving a holding penalty.
Scott Clemmensen had 40 saves and Marcel Goc also scored for Florida, which has won four of five.
The Senators, sixth in the Eastern Conference, have lost the first three games of a seven-game road trip. They are two points ahead of the New York Rangers and New York Islanders.
"When you're down to 10 games left in your season, I think that's more of a motivator than anything else," Ottawa coach Paul MacLean said. "I thought we dominated the game for the most part, but we got goalied. We've done that to other teams in the past."
Anderson stopped 15 of 17 shots in his return from an ankle injury he sustained against the Rangers on Feb. 21. He missed 18 games and did not play when he returned for Friday night's 4-2 loss at Buffalo.
"We had momentum for most of the game and we put a lot of pucks at the net," he said. "It was one of those nights we ran into a hot goaltender. Give Scot credit where credit is due. He made some big saves and stole them the game."
Clemmensen refused the compliment.
"I'm not going to say that (I stole the game) and obviously you shouldn't expect me to," Clemmensen said. "The fact of the matter is you just keep playing, you just try to stop that next shot. "
Anderson had won the previous four meetings at Florida.
"Don't discount that he's got a home here, he works out here, he's got a quality fan base and friend base that's based out of here" Florida coach Kevin Dineen said of Anderson. "So good for him, but even better for us to pop that bubble."
Ottawa's Cory Conacher scored his first goal since being acquired from Tampa Bay on Wednesday. He scored at 12:26 of the first period to give Ottawa a 1-0 lead.
Mika Zibanejad fed Jakob Silfverberg in front of the net. Silfverberg then slid the puck to Conacher, who stood next to the left post as he directed he puck into the net.
"It would be a little better to celebrate with a win," Conacher said. "I have to give so much credit to the two guys I played with — they made good plays on that play. I basically just had to finish it off and tap it in."
Goc deflected Tomas Fleischmann's wrist shot from the left point to tie the score at 1 at 1:08 of the second period. It was his fifth goal.
NOTES: Florida had six shots in the first period and four in the second period. ... The Senators also lost four straight (0-2-2) from Feb. 28-March 6.