THOMAS Bjorn's decision to treat the Open Championship as "a bit of a joyride’’ paid off today as he posted the clubhouse target with a superb opening 65 at Royal St George's.

Bjorn, 41, famously blew a three-shot lead with four holes to play when the Open was last staged here in 2003, taking three shots to escape from a greenside bunker on the 16th.

He was only sixth reserve as recently as last week before a spate of withdrawals, but made the most of his late call-up on Monday when Vijay Singh pulled out through injury, carding seven birdies and two bogeys for his lowest round in 14 Open appearances by three shots.

"It was not very nice being first reserve on Monday but I decided to treat it as a bit of a joyride if I got in,’’ said Bjorn, who played the last four holes in one under par today, compared to four over in 2003.

"It gave me a bit of a boost on Monday when I got in and it's a good start. There's a lot involved after what happened in 2003 and I was just happy to get in first of all.

"I've not had good form of late so it's a bit of a surprise to me how well I played today.’’ Bjorn held a two-shot lead over Spain's Miguel Angel Jimenez, who was approaching the end of his round, while playing partner Simon Dyson matched Bjorn's bogey on the 18th to card a 68.

Dyson was also a reserve last week before David Toms pulled out through injury, and had a cortisone injection in his back to enable him to play.

Although the wind was nowhere near as strong as during the practice rounds, scoring was still tough and US Open champion Rory McIlroy was among those having to battle hard.

McIlroy, favourite to become the youngest Open champion since 1893 following his stunning victory at Congressional last month, dropped two shots in the first three holes, but steadied the ship with a birdie on the eighth and was one over par after 12.

World number one Luke Donald, fresh from victory in the rain-shortened Scottish Open on Sunday, was level par at the same stage, but 2003 winner Ben Curtis was seven over with five to play.