By Alan Baldwin
Julia Mancuso, silver medalist in Wednesday's downhill won by U.S. team mate Vonn, was second again and Sweden's Anja Paerson, who decided to compete only at the last minute after a heavy crash the day before, battled to bronze.
"It's incredible, you always try to have positive thoughts and believe you can come back strong," said Riesch, a close friend of Vonn's and the slalom world champion who turned the tables after flopping in Wednesday's downhill. She beat Mancuso by 0.94 seconds.
"I was not nervous and that was the key because yesterday I was. It was a course to attack because it was not so difficult and the coach told us to just attack it full gas."
Vonn was fastest in the morning's downhill but would have had to produce something special to hold off Riesch. Instead, she snagged a gate in the slalom, lost a ski and went out thumping the snow in frustration.
"I'm disappointed but I went down fighting," said the golden girl of U.S. skiing, who has been center stage since she arrived in Vancouver with a shin injury. "Maria and Julia put in good runs so I knew I had to put in my all.
"I tried as hard as I could, it just didn't go my way."
Mancuso, who lay on her back like a beetle in the finish area to waggle her skis in the air in jubilation, could not believe her success.
"So far, so good," she said. "It's awesome. Seeing the leaderboard after crossing the finish line having made a couple of mistakes, I didn't believe it. It's just been an incredible week."
Paerson, who had been only 50-50 to start on Wednesday night after a spectacular crash off the final jump in the regular downhill, was only seventh after the opening run.
She raised her hands in the air and clenched her teeth as she crossed the slalom finish, slapping her bruised thighs at a job well done.
On Wednesday she had ended up on her front on the snow, grimacing in pain. A day later, she willingly dived face first again -- this time in delight at an unexpected medal.
"I was pretty scared this morning," she said. "It hurt a lot but I didn't want to miss out on an event. I am a fighter and you have to keep on smiling."
(Additional reporting by Patrick Vignal and Simon Evans)
(Editing by Ed Osmond.)