"Coming into Toronto, on Hockey Night in Canada, a divisional opponent, so many things that made this an important game," the 32-year-old said after backstopping Boston to a 3-1 win over the Maple Leafs.
Thomas was fantastic in stopping 27 of 28 shots as the Bruins took the opening game of two straight between the two clubs at the Air Canada Centre.
The Northeast Division rivals meet again Tuesday.
For the Bruins, who remain last in a very competitive division, they couldn't afford to get swept by the Leafs in the two-game set even this early in the season.
"It's important to start winning games anywhere, period, but in our division it's even bigger," Thomas said. "Toronto was 10 points ahead of us before this game so these are four-point games. They're huge."
Brad Boyes, Marc Savard and Petr Tenkrat scored Saturday for the Bruins (10-9-2), who have taken two of three against the Leafs this season.
Mats Sundin, in his return after a seven-game absence, scored the lone goal for the Leafs (13-8-4), who were dominating the Bruins in the third period before Boyes, a former prospect, scored the insurance goal with 4:16 remaining.
Andrew Raycroft was solid in net for the Leafs, stopping 22 shots to limit what could have been a worse result.
Sundin, who recovered from an elbow injury, started the game between John Pohl and Chad Kilger but by the second period had been reunited with Nik Antropov and Alexei Ponikarovsky.
"It felt like I haven't played in three weeks," Sundin said. "The timing and all that is going to take a few games, obviously, but it will get better from here on."
Still, it was Sundin who finally solved Thomas when he banked a rebound behind him during a mad scramble on a Leafs power play at 12:04 of the third period, the captain's ninth goal this season. The elbow looked fully healed.
"It felt really good, actually," Sundin said. "My arm felt great. It's more (my) legs and timing and shooting, holding onto the puck and knowing where everybody is on the ice (that needs work)."
The Leafs then pressured in waves but couldn't get the equalizer. Boyes, parked alone in front, slipped a shot between Raycroft legs to quiet the crowd of 19,473.
The Bruins came roaring out the gates and dominated the Leafs for the opening seven minutes and it produced a goal at 6:04 when newly acquired Stanislav Chistov fed a pretty pass to an onrushing Tankrat who beat Raycroft top corner on the glove side from the slot.
Savard made it 2-0 just over eight minutes later during a Boston power-play when he one-timed a wrist shot, again glove-side and top corner on Raycroft.
"They played better than we did in the first period, and when you're down a couple goals against any team, it's always tough to get back," Sundin said. "It seems like they had a little bit more energy than we did, for sure."
Late in the period, Darcy Tucker hammered big Zdeno Chara with a clean but thunderous check, which led to a centre-ice tussle between Tucker and Bruins blue-liner Paul Mara.
Tucker felt Mara jumped him.
"I didn't see him coming," Tucker said. "From what I hear, he had his gloves off before he got to the pile."
The Leafs lost defenceman Pavel Kubina halfway through the second period when he took a puck in the face. He returned for one shift late in the third period and should be good to go Tuesday.
"He got an awful lot of stitches," said Leafs coach Paul Maurice.
Notes: With Sundin activated from injured reserve, the Leafs will place rookie defenceman Jay Harrison on 48-hour waivers at noon ET Sunday. If he isn't claimed by another team by noon ET Tuesday, he'll report to the AHL Marlies ... The Bruins may possibly recall goalie Hannu Toivonen from AHL Providence in time for Tuesday's rematch. Goalie Brian Finley remains day to day with a groin problem so Phil Sauve dressed as the backup to Thomas for the second straight game ... Bruins defencemen Nathan Dempsey and Milan Jurcina were healthy scratches for Boston while Toronto didn't dress blue-liner Brendan Bell or forward Aleksander Suglobov ... The Leafs went 4-2-1 in Sundin's absence.