But Willstrop wasn't one to give up and he worked his way back to return to where he truly belongs. And the 33-year-old had to summon those fighting qualities against Egyptian young gun Ali Farag in the PSA Dubai World Series Finals at the Dubai Opera.
And having come on the right side of the result, a 4-11, 11-9, 11-6 verdict, Willstrop stands at the cusp of a possible Dubai title.
But standing in Willstrop's way is none other than world No.1 Karim Abdel Gawad, whom he meets in a lip-smacking semifinal.
And Willstrop, silver medallist at the Commonwealth Games in New Delhi in 2010 and Glasgow in 2014, has the chance to avenge the defeat he suffered at the hands of the Egyptian at the JP Morgan Tournament of Champions in January this year.
But it almost wouldn't have been for Willstrop as he found himself second best to Farag, a replacement for three-time world champion Ramy Ashour, in the first game. But then, Willstrop pulled it all together to take the second and the decider.
"I didn't think I did too badly really, he was just so good. It was maybe a little bit short when I was hitting to the back and I thought that all I could do at the start was to stay in it. I had to have a bit of faith that, despite the fact it's gone wrong on the scoreboard, I could turn it around," Willstrop said after the match.
"You've got to regroup and you can't let it get to you mentally. I thought that I just had to win the two games, it's as simple as that," he added.
The Yorkshireman also gave credit to Farag for the way he played and said that the 25-year-old, who had halted defending champion Gregory Gaultier's 27-match winning streak in the first round, has a brilliant future ahead of him.
"People throw it around when they say that someone can become World No.1 and it doesn't happen that easily, but Ali's an awesome squash player and a credit to the game as well," said Willstrop.
Willstrop will take on world champion Karim Abdel Gawad in the semis.
Gawad began the tournament with a defeat to Rosner, but qualifies top of Group A after following up a day two win over 2010 finalist Nick Matthew with victory over compatriot Marwan ElShorbagy, which sees the World No.1 go ahead of Rosner in the group due to a higher games won percentage.
"I didn't have the best start to the tournament," admitted Gawad. "I would say it's the first time on court where I got too excited and didn't start the right way. I had no pressure on me afterwards and I just wanted to enjoy playing in such a great venue."
Meanwhile, defending champion Gaultier ended the tournament without a win, after going down to Mohamed El Shorbagy 10-12, 7-11.
On the women's side, France's Camille Serme takes on Egypt's Nour El Sherbini, while Nouran Gohar, also of Egypt, meets England's Laura Massaro in what could be an interesting battle.
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