Jack Draper's Indian Wells title defence came to a contentious conclusion in the quarter-finals after umpire Aurelie Tourte penalised him for hindrance against Daniil Medvedev.
The pivotal incident occurred with the second set locked at 5-5 and Draper trailing 0-15 on his own serve.
The British number one briefly extended his arms outward during a rally, believing Medvedev's forehand had landed beyond the baseline.
Despite the rally continuing for seven more shots before Medvedev missed a backhand, the Russian requested a video review.
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Tourte studied the footage on her tablet before ruling against Draper, explaining that he had done "something different in the rally than you would normally do".
Stadium Court 2 erupted in boos as the decision was announced, with spectators jeering Medvedev at the changeover and again following his eventual 6-1, 7-5 triumph.
The 24-year-old appeared visibly drained following his gruelling third-set tiebreak victory over Novak Djokovic less than 24 hours earlier.
Medvedev seized control from the outset, breaking Draper's opening service game when a net cord fell fortuitously in his favour at break point.
Jack Draper's Indian Wells title defence came to a contentious conclusion in the quarter-finals after umpire Aurelie Tourte penalised him for hindrance
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The former world number one raced into a 4-0 advantage within just 15 minutes, firing winners both down the line and across court with clinical precision.
Draper managed to hold serve and avoid a bagel, making it 5-1, but Medvedev wrapped up the opener in a mere 25 minutes.
The second set proved more competitive, though Draper's serve remained under constant pressure.
It took the Briton 49 minutes to fashion his first break point opportunity, which Medvedev saved with three consecutive aces.
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The defeat will see Draper tumble from 14th to 26th in the world rankings on Monday, surrendering the British number one position to Norrie
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Draper was gracious in defeat, telling BBC Sport that Medvedev "was the stronger player fair and square" and insisting he harboured no ill feeling towards his opponent.
Draper said: "I don't think I did enough to hinder him, but at the end of the day I did make a slight thing with my hands. I think he's played the rules quite well. The rally carried on and I was able to win the point so I don't think I should have lost the point. I think it's pretty harsh."
The pair shared a lengthy but amicable exchange at the net, with Medvedev offering: "If you're mad at me, I'm sorry."
Medvedev acknowledged the incident left him uncomfortable: "Do I feel good about it? Not really, but I also don't feel like I cheated. I let the referee decide."
British involvement in the singles draw concluded when Cameron Norrie fell 6-3, 6-4 to world number one Carlos Alcaraz in the quarter-final.
Draper conceded that his body had simply given out after the emotional and physical toll of defeating Djokovic
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Norrie battled admirably against the Spaniard but was ultimately outclassed by the two-time Indian Wells champion.
Medvedev will now face Alcaraz in the semi-finals.
Draper conceded that his body had simply given out after the emotional and physical toll of defeating Djokovic.
He said: "Today I ran out of steam and I wasn't able to compete again a day later with one of the best players in the world, and that's just totally normal."
The defeat will see Draper tumble from 14th to 26th in the world rankings on Monday, surrendering the British number one position to Norrie.
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