Colin Montgomerie began his quest to secure an eighth Order of Merit title with a 67 at the Volvo Masters to share the lead with Ian Poulter.
GB&Ire unless stated
-4 C Montgomerie, I Poulter
-3 L Donald, S Garcia (Sp), JM Olazabal (Sp)
-2 R Karlsson (Swe), S Webster
-1 B Dredge, N Fasth (Swe), G Havret (Fr), R Jacquelin (Fr), M Lafeber (Ned), H Stenson (Swe)
+1 M Campbell (NZ)
The 42-year-old Scot carded five birdies and holed a 110-yard wedge shot to eagle the eighth hole.
US Open champion Michael Campbell, the only man who can deny Montgomerie the Merit title, began with a one-over 72.
Defending champion Poulter, who has not won since his victory at Valderrama 12 months ago, collected five birdies.
Paul Casey set the early pace, moving to four under after seven with an eagle and two birdies in four holes, before a double bogey at the 16th resulted in a one-under 70.
Montgomerie birdied the first with a seven-foot putt, and went two ahead of Campbell when the New Zealander failed to get up and down from a bunker.
Montgomerie also birdied the short third, but dropped a shot at the fifth when, from a sloping lie, he found a greenside trap.
He got that shot back immediately with a two at the sixth, and after his memorable eagle, when the ball span back into the cup, two putts from the edge of the long 11th green gave him another birdie.
Montgomerie had a six-foot chance to birdie the 17th after a neatly controlled pitch, only for the putt to stay above ground.
But at the last his approach finished five feet away and the putt found the centre of the hole.
The gladiators shake hands on the first tee at Valderrama.
Campbell recorded his third bogey of the day at the last when he found a grassy lie to the left of the fairway and, having raced his 20-foot par putt five feet past, was relieved to drop only one shot to finish on one over.
Luke Donald curled in a deft 15-foot effort at the fifth for his third birdie, and moved to four under at the turn, before playing the back nine in one over to finish with a 68.
Sergio Garcia was another to lament the final hole, his run of four birdies on the back nine brought to an abrupt halt when a six-footer for par missed on the right to bring him back to three under.
Montgomerie admitted that he had been feeling under pressure in the build-up to the tournament.
"It's pleasing because the last few days have been difficult," he said. "I've got everything to lose if you like, but I love this golf course and I got rid of the anxiety in the first three holes.
He paid tribute to former Ryder Cup captain Bernhard Langer, who selected him for the Ryder Cup in 2004 when he was only 27th on the list.
"If I hadn't been picked I would not be here now," Montgomerie said. "It was crucial for my career. It was going in the opposite direction and he gave me the opportunity."
Poulter, who beat Garcia in a play-off to win the title a year ago, was pleased to make a better start this time around.
"It's four better than when I won, so I'm very happy," he said. "It's nice to get off to a decent start - I was three over after nine last year."
The extravagant 29-year-old is determined to maintain his record of at least one victory each season since his rookie year in 2000.
"I have no option other than to win. It was exactly the same last year - there is no other focus on my brain right now and that's a lesson I have to learn every single week.
"I need to tell myself I have to win this. I am sure Tiger does. I have to win to keep my record going. There's one word - win."
Despite the five shot gap, Campbell maintained an optimistic air. "There's a long way to go," the 36-year-old said. "Three rounds over this course can change things a lot."