Meanwhile, de Minaur's fellow Australian Aleksandar Vukic enjoyed one of the best wins of his career on Friday, knocking out top seed Frances Tiafoe to reach the Almaty Open semi-finals.
The contrasting fortunes of the two Sydneysiders emerged on a busy late-season tennis day around Europe with the business end of three ATP tournaments taking place.
did Gaston just hit shot of the year?!🤯— ATP Tour (@atptour) @EuroTennisOpen | #EuropeanOpen pic.twitter.com/1woFvveBpQOctober 18, 2024
Yet Antwerp top seed de Minaur was perhaps the most frustrated player of the lot as he missed out on a golden opportunity to gain valuable points in his bid to be one of the top eight men's players who qualify for the season-ending championship in Turin.
Earlier on Friday, the door had been left ajar for de Minaur to gain points on Andrey Rublev, currently eighth in the 'Race to Turin' standings, as the Russian top seed was knocked out of the quarter-finals of the Nordic Open in Stockholm 7-6 (7-5) 7-6 (7-5) by the ageless Stan Wawrinka.
At No.9 in the standings, de Minaur could have closed the gap by reaching the semi-finals at the European Open in Antwerp against French world no.77 Gaston, who'd never beaten a top-10-ranked player before.
But Gaston, who'd also defeated 'Demon' at a fiery French Open match in 2022 when the Aussie complained about a raucous Roland Garros crowd "going over the line" in support of the maverick home favourite, again defied the odds - and injury - and a hugely entertaining quarter-final.
Although needing a second-set medical timeout for what seemed to be a groin injury and never moving easily after that, Gaston still uncorked some fizzing shots to defy a rusty de Minaur, who was playing in only his second tournament in three months since his injury-hit Wimbledon.
Nothing topped the glorious moment in the opening set when southpaw Gaston raced back to retrieve a near-perfect de Minaur lob and somehow, with back to the court, whipped a blind winner from over his shoulder past the astonished Aussie, who could only applaud.
De Minaur looked hot favourite in the deciding set as Gaston hobbled around between points but he somehow raised his game, sealing only his second break in the final game with a fabulous backhand winner down the line to prevail 6-3 3-6 7-5 after two hours nine minutes.
Aleksandar Vukic has made it to his third ATP semi-final in Almaty. (AP PHOTO)
Earlier in Kazakhstan, Vukic knocked out American top seed Tiafoe 6-2 7-6 (13-11), prevailing in a dramatic tiebreak during which he let four match points slip while saving two set points of his own.
"Pretty overwhelmed, that tiebreak was pretty crazy," beamed the Australian world No.85 afterwards.
"We were both a little bit nervous and the crowd was really getting into it, the atmosphere was great. I guess this is what it's all about, you don't feel emotions like this anywhere else. Happy to get through and go again tomorrow."
In his third ATP semi-final, Vukic will face Russian Karen Khachanov in Saturday's last four.
How was he planning to prepare? "Might go to the driving range next door to our hotel, unleash some balls to get some emotion out of me," smiled Vukic.
