"Coming off back-to-back nights, you want to get off to a good lead. We were able to do that with two early first ones," Thornton said. "We just kind of rolled on after that. It is always nice to get a 2-0 lead like that when you are playing back-to-back."
Hertl leads the team with 12 goals and has scored in successive games for the second time this season.
Niemi got the night off and Alex Stalock stepped in with 30 saves against the Oilers to improve to 3-0-0.
The Blackhawks (13-3-4) are coming off a 7-2 loss Saturday at Nashville. They hadn't dropped a regular-season game by more than two goals since their first regulation loss last season -- a 6-2 defeat at Colorado on March 8.
"We got outworked," center Jonathan Toews said. "We didn't do the things we needed to. We didn't win our battles, especially in the right areas we needed to win them in."
Chicago fell behind 4-0 late in the second before Patrick Kane got the Blackhawks on the board with his team-leading 11th goal. Kane has nine points during his current six-game point streak and also has a five-game streak going against the Sharks.
Brandon Pirri made it 4-2 early in the third, but Nashville closed it out with three unanswered goals.
"It was a free night for them offensively, we were very gracious," Blackhawks coach Joel Quenneville said.
Chicago played without forward Marian Hossa, who was sidelined by a lower-body injury. Quenneville said there is a chance he could face the Sharks.
Nikolai Khabibulin made just his fourth start in goal, but he exited late in the first period with an injury after allowing two goals on eight shots.
Corey Crawford wasn't much better. Chicago's usual No. 1 goalie allowed the next five goals on 22 shots.
With Khabibulin expected to be out for "a bit," according to Quenneville, and struggling when he has played, Crawford figures to start against the Sharks. He's is 2-0-0 at home in his career against San Jose.
The Sharks and Blackhawks, along with St. Louis, are tied with a league-best 3.50 goals-per-game average.
The Blackhawks swept the three-game season series with the Sharks last season, including a 2-1 home win on Feb. 22 in the most recent meeting.