Willstrop forced to battle his way into quarters in Philadelphia.

But it was the second tough match in a row the world No 1 was forced to endure, having taken 80 minutes to see off the challenge of former Chapel Allerton SC regular Alister Walker in Saturday’s first round.

It got no easier against world No 11 Selby on Monday, with Willstrop having to come back from losing the opening game before closing out the match 9-11 11-4 12-10 11-5 in 81 minutes.

He now faces a last eight clash tonight against Egypt’s Mohamed El Shorbagy, who was involved in an epic struggle with Australia’s Cameron Pilley before winning 10-12 11-8 12-10 10-12 11-4 after 92 minutes.

Sheffield’s Nick Matthew also made it through to the last eight with a 11-2, 11-5, 15-13 win over fellow Englishman Adrian Grant.

The world No 2 could now face Amr Shabana in the next round if, as expected, the Egyptian former world No 1 defeats the Laurens Jan Anjema from the Netherlands.

Elsewhere in the second round, France’s Gregory Gaultier made it through to the last eight after defeating Spain’s Borja Golan, winning 11-7 11-4 11-7 in just under an hour.

In the women’s draw, Harrogate’s world No 4 Jenny Duncalf began her campaign in style, navigating her way through a tricky first round tie against Australia’s Rachael Grinham.

It took Duncalf – seeded three for the event – just 33 minutes to see off her opponent, closing out to win 11-5 11-8 11-4.

She will now face New Zealand qualifier Joelle King, who caused something of an upset in defeating Egyptian seventh seed Nour El Sherbini 12-10 11-6 11-5.

If successful, Duncalf can expect to face longstanding world 
No 1 Nicol David in Thursday’s semi-finals.

The Malaysian sensation took just over 40 minutes to defeat France’s Camille Serme 11-6 11-8 11-8. She will now face England’s Alison Waters, who edged out eighth seed Natalie Grinham.