In his first game after signing the deal, Mason allowed four goals and was pulled in the second period in favor of Ray Emery before the Flyers rallied for the win.
Mason had a breakout first NHL season, earning rookie of the year honors and recording 10 shutouts with Columbus in 2008-09.
He hadn't again played to that level before being dealt to the Flyers last April 3.
Mason said having the extension should make him relax more.
"It's nice to have that in the rearview mirror now," he said. "Just looking forward to being here for the . . . foreseeable future."
In seven appearances with the Flyers late last season, he was 4-2 with a 1.90 goals-against average and .944 save percentage. Mason entered Saturday's game 19-11-5 this season with a 2.48 GAA and .917 save percentage.
"We acquired him last year from Columbus and viewed him as a good No. 1 that kind of lost his way," Holmgren said. "I think he has fit in with our team."
As for how they decided on the duration of the contract, Holmgren said: "We talked about shorter, we talked about longer than that. It just came where it kind of matched up."
Mason's teammates were naturally ecstatic.
"Obviously, he has played so well for us, and it's good to have him locked up for three years," forward Jake Voracek said.
Goalie Anthony Stolarz, a Flyers second-round draft pick in 2012, suffered a gruesome skate cut to the back of his leg while playing for the London Knights of the Ontario Hockey League in Friday's 3-1 loss to the visiting Saginaw Spirit.
Holmgren said that Stolarz required 55 stitches but that he escaped even a much more serious injury. According to Holmgren, Stolarz, who turns 20 on Monday, will be out four to six weeks. Holmgren considered it a positive sign that Stolarz will be allowed to ride a stationary bike in a few days.