England's James Willstrop will return to the top of the PSA world rankings in March after reaching the semi-finals of the Davenport North American Open in Richmond, Virginia.
The top seed's quarter-final opponent, Egypt's Amr Shabana, was forced to concede the match in the PSA World Series squash event at the Westwood Club early in the second game - after just 12 minutes - because of a knee injury.
By reaching the last four, Willstrop earned enough ranking points to regain the world number one position from his great English rival Nick Matthew, the world champion from Sheffield.
Willstrop, who topped the rankings for the first time in his career in January after three PSA World Series event wins in Hong Kong, Kuwait and India at the end of 2011, said: "It's great news to be back on top - but I would find it very difficult to celebrate because nobody wants to win a match that way."
Willstrop meets French ace Gregory Gaultier in the semi-finals, a re-run of the 2008 Virginia final which the Englishman won. Gaultier overcame young Egyptian qualifier Karim Abdel Gawad, winning 11-6, 11-2, 11-6 in 39 minutes.
"I am feeling good this week," said the Frenchman. "When you are well looked after, and feeling relaxed, and nothing is going on to upset your brain, then you can play well."
In the other semi-final, Matthew meets Ramy Ashour in a re-run of the last three NAO finals. Ashour won in 2009 but Matthew has won the last two events - and is hunting down a hat-trick of titles this year.
Ashour confirmed his return to peak fitness with a devastating victory over fellow Egyptian Karim Darwish. After the first two games were shared, Ashour wore down his opponent and powered through the third and fourth, making experienced former world number one Darwish look demoralised at the end.
Ashour said: "It's never easy to beat Karim. We had breakfast together and spent a lot of time together during the day, but as soon as reached the court we know that we have a job to do and try to be as professional as possible."
Matthew, who had struggled to hit top form in the first two rounds, beat battling German Simon Rosner in four hard games.
The current world number one dominated the opening two games and seemed set to wrap things up quickly as he led 8-4 in the third, but Rosner recovered to win a succession of breathtaking rallies. He won the game 11-9 but the effort clearly took its toll as Matthew stayed in front throughout the fourth.
Matthew said: "I started well in those first two games but I need to step up another notch against Ramy. He is playing very well this week. It will be strange playing him in the semis after meeting him in the past three finals."
RESULTS: PSA World Series Davenport North American Open, Richmond, Virginia, USA
 James Willstrop (ENG) bt  Amr Shabana (EGY) 11-5, 2-0 ret. (12m)
 Gregory Gaultier (FRA) bt [Q] Karim Abdel Gawad (EGY) 11-6, 11-2, 11-9 (39m)
 Ramy Ashour (EGY) bt  Karim Darwish (EGY) 12-10, 8-11, 11-5, 11-3 (56m)
 Nick Matthew (ENG) bt Simon Rosner (GER) 11-7, 11-6, 9-11, 11-6 (63m)
 James Willstrop (ENG) v  Gregory Gaultier (FRA)
 Nick Matthew (ENG) v  Ramy Ashour (EGY)