It was the end of the run for unseeded Leeuw who made his breakthrough in the opening round when he dismissed defending champion Shawn Delierre.
“The real match started in the second game,” reported Yann Perrin, the Frenchman who lost to Pett in the previous round. “There were long rallies and Clinton tried to take the ball earlier and got on to the volley more – and it was working.
“He was to put more pressure with his backhand drop, and he won the second. After the third and the fourth, it was really close; but a few errors from Clinton gave the opportunity to Olly to finish the point.
“The last point exemplified what the match was all about – a great rally and some fantastic retrieving, ending with a cross-court flat dead nick from Olly reaching back under pressure high on the forehand.”
Pett, the 23-year-old world No58 from Sussex, was delighted with his 11-7, 7-11, 11-8, 13-11 win: “It was a hard fought match! Clinton was playing with a lot of confidence and I was nervous because I knew I was next on his to-do-list! Luckily, I was able to squeeze some mistakes out of him and take the match.
“To be honest, the longer the match went on the more nervous I became so I was very happy to get the win. Clinton was running me around the court for a good portion of the match, thankfully I enjoy burning calories. I love London Squash, everyone is really nice and the gym is great!”
Rising Canadian star Schnell reached the semis after upsetting third seed Jan Koukal in the previous round.
“Couldn’t pull another upset tonight, but overall a great event,” tweeted the 20-year-old from Calgary after his Nash Cup exit.
World No31 Illingworth is celebrating the 18th PSA Tour final of his career – and his third in a row. By contrast, it will be only the third of Pett’s career – but the Englishman boasts 100% success in his previous two!
 Julian Illingworth (USA) bt Andrew Schnell (CAN) 7-11, 11-8, 11-7, 11-9 (56m)
 Olivier Pett (ENG) bt Clinton Leeuw (RSA) 11-7, 7-11, 11-8, 13-11 (56m)