Dominic Thiem denied Roger Federer a record sixth Indian Wells title, beating the Swiss great 3-6, 6-3, 7-5 on Sunday to claim his first ATP Masters 1000 crown.
The 25-year-old Austrian, ranked eighth in the world, had fallen in two prior Masters finals, both in Madrid.
But he rallied for a third career win over Federer in five meetings, his first over the Swiss on hard courts.
"It feels just unreal what happened in this 10 days," Thiem said. "I came from a really bad form in all categories, and now I'm the champion of Indian Wells.
"It feels not real at all," added Thiem, the first Austrian to win a masters 1000 title since Thomas Muster at Miami in 1997.
Thiem earned the crucial break in the 11th game of the final set, connecting on two sharply angled passing winners off of Federer drop shots to give himself a break point which he converted with a stinging forehand winner.
"He stayed cool under pressure there," Federer said. "When he got up to the ball, stayed calm, made the shot."
Thiem sealed the match after two hours and two minutes when Federer's backhand found the net and will now return to a career-high ranking of fourth in the world, bumping Federer down to fifth.
It was the second year in a row that Federer was denied in the Indian Wells final. In 2018 he missed out on three championship points as he fell to Argentina's Juan Martin del Potro in the title match.
Federer, fresh off a remarkable 100th career title in Dubai, remains tied with Novak Djokovic for the most Indian Wells victories with five.
Thiem claimed his 12th career title -- as he noted at the trophy ceremony when he acknowledged Federer.
"I think it's not my right to congratulate you, you have 88 more titles than me," Thiem told Federer as he accepted the trophy, calling it a privilege to play against the 37-year-old superstar.
"It's tough against Roger, Rafa (Nadal), Novak (Djokovic)," Thiem said. "Because you have to beat not only the player but somehow also the great aura they all have, all these titles they have won.
"So you have to play somehow double-good to beat them."
Thiem was under attack early, saving three break points before succumbing on a fourth in the second game as Federer raced to a 3-0 lead.
Federer led 4-1 before Thiem clawed a break back, but Federer responded with another hard-won break for a 5-3 lead and captured the set with a service winner.
Coming into the contest Federer had won 20 straight finals when claiming the opening set.
But Thiem was not about to go quietly, saving break points for a 2-1 lead in the second and breaking for a 3-1 lead as the Swiss suddenly couldn't put a first serve in.
A hold at love put Thiem up 4-1 and on the way to forcing the third set.