Vonn defended her lead from the morning downhill with a solid slalom leg to clock a combined two-run time of 2 minutes, 28.35 seconds.
“It was a really satisfying win. I was happy with my downhill run but I knew it was going to be tough to hang on,” Vonn said.
Maze of Slovenia was 0.41 seconds back and third-place Nicole Hosp of Austria trailed Vonn by 0.58.
Vonn earned 100 World Cup points for her 48th career World Cup victory and leads Maze by 302.
Vonn won the super-combined title the past two years. She has seven victories this season in her quest to regain the overall crown.
“It was really important today,” Vonn said. “If I were to go out (in slalom), I knew that Tina would be within striking distance, so I had to stay on the podium. I tried to ski smart.”
Maze trailed Vonn by 1.41 seconds in downhill.
“I tried to be fast and be close to Lindsey,” she said. “I lost too much time. Super-combined is like that, and if you don’t do well in one (discipline), you lose.”
Vonn held her nerve when Maze and Hosp put down the two fastest slalom runs after they finished the downhill sixth and seventh, respectively.
“It definitely wasn’t pretty skiing, but I made it,” Vonn said. “There aren’t many parts of slalom I’m good at, but on the flats is one of them.”
Elisabeth Goergl of Austria was second in downhill, 0.61 behind Vonn, but skied out in the slalom.
Defending overall champion Maria Hoefl-Riesch of Germany had a big mistake midway down the slalom and hiked up the mountain to resume her run. She finished 21st, more than five seconds behind the leader.
The Olympic champion in super-combined was third after the morning run.
Hoefl-Riesch is winless this season after denying Vonn a fourth straight giant crystal globe last year.
Hosp won the overall crown in 2006-07 before Vonn’s winning streak began, but has sustained a series of injuries since. The 28-year-old Austrian got her first podium finish this season, and just her second since March 2009.
American teammates Leanne Smith and Julia Mancuso dropped in the standings after being fourth- and fifth-fastest in downhill.
Mancuso, the Olympic silver medalist in super-combined, finished 13th, 3.82 behind Vonn. Smith placed 18th, 4.74 back.
Both were upbeat about their prospects in Saturday’s marquee downhill race.
“I tried to push it today to see where I can be perfect for (Saturday),” said Mancuso, who is seventh in the overall standings. “I’m happy with where I am.”
Smith said her form was heading “definitely in the right direction.”
“I know I have the speed, but there’s still a few things to fix,” Smith said. “I just need to be cleaner in a couple of places.”
The St. Moritz event ends Sunday with the second of the season’s three scheduled super-combined events. The super-G and slalom legs are a makeup for a canceled race last month at Val d’Isere, France.