It took 122 minutes for Nick Matthew to emerge triumphant in the first all-English men's final for 70 years.
Matthew reached the final without dropping a game, but it was Willstrop, last year's runner-up, who took the early advantage - winning the first game in convincing style.
However Matthew, who won the worlds oldest and most prestigious squash title for the first time in 2006, battled back to take the second. The next two games were also shared - with Willstrop visibly tiring at the end of the fourth as he made three successive unforced errors.
In the decider, a gladiatorial encounter between two determined Englishmen, Matthew built up a 6-2 lead before Willstrop delighted the packed crowd by coming back to overtake his opponent, eventually reaching match-ball at 10-9.
But former champion Matthew was not about to throw in the towel. The 29-year-old reclaimed the advantage before going on to clinch the title on his first match-ball, winning 8-11 11-8 7-11 11-3 12-10 to claim the historic trophy for the second time.
"That was a fantastic match," said the new champion as he collected the trophy. "I want to thank James. I think you deserved it - you were the best player on the night, but I gutsed it out!"
Matthew, who boasts a career-high World No.5 ranking, then admitted that he had been suffering with a back injury during the tournament: "I nearly didn't play the quarter-final match. I spent about five hours in the physio room before that match - and it's thanks to EIS (English Institute of Sport) physio Jade Elias that I came through. Jade, you're a star!"
Asked later if he thought he was a better player than when he first won the coveted title in 2006, since when he has undergone shoulder surgery, Matthew said: "I was a better squash player yesterday, in the semis, than I was today.
"Today was best in terms of guts and determination.
"I don't know how my body got through this week. I'm just shattered by the effort. The last few points were a blur.
"I'm amazed I ever got to the final, let alone win the title," concluded the new champion.
Issued by

National Squash Centre, Manchester
Men’s Championship Final:
[4] Nick Matthew (ENG) bt [10] James Willstrop (ENG) 8-11, 11-8, 7-11, 11-3, 12-10 (122m)
England No.1 Nick Matthew defeated compatriot James Willstrop 8-11 11-8 7-11 11-3 12-10 to win the internationalSPORTgroup British Open - Manchester 2009 at the National Squash Centre in Manchester.