After that he was flawless, making 23 saves for the Blues in a 4-1 win.
"I was hoping to get a few shots early in the game, but not the way it was," Halak said. "I started feeling more comfortable as the game went on, especially in the second I made some saves that got my confidence back and I started feeling better."
Brenden Morrow scored twice and Vladimir Tarasenko and Magnus Paajarvi also scored, as the Blues continued their mastery of the Sabres (5-17-1). St. Louis has won 13 of 15 games against Buffalo since 1999.
Tyler Ennis scored the Sabres' goal, as Buffalo lost at home after consecutive home wins last week.
Halak was pulled from Sunday's loss in Washington after allowing three goals on six shots in just 16 minutes. St. Louis coach Ken Hitchcock liked his goaltender's response.
"Bottom line he played really well," Hitchcock said. "We needed him and he played good. That's what's good for Jaro. He stepped back and he made some big saves today. That's a good sign for us."
At 14-3-3, the Blues are off to their best start through 20 games in franchise history.
The Blues' league-best power play stayed productive, scoring in their fourth straight game. It's a stretch that's seen the Blues go 6 of 17 with the man advantage.
"We drew a couple penalties, got the first one on the power play to make it 2-1 and hung on from there," Morrow said. "They were able to put a lot of pressure, throw some pucks at our net and we gave up more shots than we usually do."
St. Louis is 8-1 in its past nine trips to Buffalo. The Blues improved to 7-2 against Eastern Conference teams, outscoring opponents 31-17.
Though the Blues outshot the Sabres 31-24, they got off to a slow start.
After a dump of the puck into the Blues' zone off the opening faceoff, Ville Leino stripped the puck from Jay Bouwmeester below the left faceoff circle and found Ennis, who beat Halak with a low shot to give the Sabres an early lead.
Though Halak may have been jittery, St. Louis responded well to the quick setback. The Blues tied the game less than a minute later when Morrow pounced on a rebound and beat Ryan Miller at 1:09 of the first.
"They got off to a great start, got a break early and we got one right back early that the changed the momentum back for us," Morrow said.
Tarasenko scored a power-play goal with 36 seconds to play in the first period on a pass from T.J. Oshie, who collected his own blocked shot.
Buffalo has been outscored 31-4 in the first period this season.
The Sabres nearly equalized in the second period, but Halak used his right pad to deny Leino, who was facing an open net.
"I gave up the rebound and just wanted to get there with my pad and lucky for me he didn't raise it over my pad and I was able to get there," Halak said. "It was a key save for me and we get another chance going the other way and we score. Could've been 2-2, but instead it's 3-1 and it was a huge goal for momentum."
Morrow's second of the game came when Cody McCormick lost the puck behind the Buffalo net.
"That was a pretty sick snipe," said Stewart, who missed the morning skate with flu-like symptoms. "He was sitting there in the slot all alone and he's not going to miss from there.
It was Morrow's first multi-goal game since April 17, when he scored twice against Montreal. Stewart had two assists.
The Sabres couldn't beat Halak again and interim head coach Ted Nolan saw a gulf between his team and the Blues.
"You could tell the difference between some of the younger players we have and some of the more mature players they have," Nolan said. "So it's just part of maturing."
Defenseman Mike Weber returned to the Sabres' lineup after missing 10 games with a hand injury suffered Oct. 25 against Florida.
Blues C Patrik Berglund missed his second straight game with an upper-body injury. ... The Sabres sent D Rasmus Ristolainen, LW Johan Larsson and C Mikhail Grigorenko to their American Hockey League affiliate in Rochester on Tuesday. ... Buffalo also sent D Nikita Zadorov to the London Knights of the Ontario Hockey League.