Westwood paired with David Howell to down Jose Maria Olazabal and Continental Europe captain Seve Ballesteros, 2-up. Casey teamed with Brian Davis to beat Ignacio Garrido and Miguel Angel Jimenez, 2 and 1.
Alex Cejka and Raphael Jacquelin gave the Continental European team their only full point Thursday when they beat Justin Rose and Ian Poulter, 4 and 3.
GB&I captain Colin Montgomerie and 1999 British Open winner Paul Lawrie halved their match with Fredrik Jacobson and Niclas Fasth. Phillip Price and Padraig Harrington scored a 2-up victory over Continental European team Sergio Garcia and Thomas Bjorn.
'We would definitely have taken that if you had offered us a two-point lead at the start of play so it has been a pretty good first day for us,' said Montgomerie. 'The competition is as intense as you would expect but the standard of play has been excellent.'
Westwood and Howell fell 1-down when Olazabal birdied the par-3 fourth at Campo de Golf Parador El Saler. Howell responded with a birdie at the next and Westwood gave the English duo a 1-up advantage with a birdie at the sixth.
Ballesteros managed to square the match with a birdie at the eighth. After the two teams split the 10th and 11th holes, Westwood took over. He birdied the 13th and 14th to give his team a 2-up lead and held them there with pars on the next two holes.
The Spaniards tried to come back to gain a 1/2 point as Olazabal birdied 17 from 10 feet out to get within 1-down. However, Howell hit a magnificent shot within three feet of the cup on 18 and made the birdie for the 2-up victory.
Davis and Casey had a similar start as they fell 1-down when Garrido birdied the third. Garrido rolled in another birdie at the sixth to give his duo a 2-up lead.
Casey rallied with birdies on Nos. 7 and 9 to square the match. Jimenez won the 10th and 12th with a birdie and par respectively. In between, Davis birdied the par-5 11th. Casey drained his third birdie of the day at No. 13 to square the match.
After Davis and Garrido halved the 14th with birdies, Casey birdied the 15th to give his duo a 1-up lead. The Englishman followed with a 12-foot birdie on 17th to claim the 2-and-1 victory.
In the fourth match, Monty picked up a birdie at the first to grab a quick lead for the Scottish duo. Lawrie extended their lead to 2-up with a birdie at the fourth.
The Swedes fought back with a pair of birdies to square the match. Fasth cut the deficit to 1-down with a birdie on the sixth and Jacobson squared the match with a birdie on the eighth.
Lawrie gave the Scotsmen a 1-up lead with a birdie on the par-3 ninth. Jacobson evened the match with a birdie at the par-5 11th. They halved the final seven holes, including birdies by both teams on Nos. 15, 16 and 17 to split the point.
'I think myself and Paul's better ball score of 65 was about the worst of the day which gives you a good indication of the standard of play, but as always this is turning out to be a great contest on an excellent golf course at a wonderful venue,' Montgomerie said. 'I am already looking forward to the next three days.'
In the anchor match, Harrington was on fire on the front nine running off three birdies and an eagle between Nos. 4 and 7 to give his duo a 4-up lead.
Garcia began to cut into that deficit with a birdie at the ninth. He cut it to 2-down with a birdie on No. 12 and the Spaniard birdied the 14th to get his duo back within 1-down.
Harrington birdied the 15th to move back to 2-up, but Bjorn birdied the next to get back to 1-down. Harrington rolled in a birdie putt from over 20 feet out at the last for the 2-up win.
'I definitely got off to a fast start and that helped keep me going,' Harrington said. 'I seemed to be hitting them close and didn't seem to be missing too many putts either which left our opponents a bit too much to do on the back nine.'
'Padraig played unbelievably well,' said Garcia. 'We did well turning for home but he had left us just too much to do.'
Jacquelin and Cejka secured the easiest win over Rose and Poulter. Cejka and Jacquelin combined to birdie five of the first six holes, all of which they won.
Jacquelin drained his fourth birdie of the day on No. 9 to move his pair 7-up through nine. The two teams halved the following two holes.
Standing 7-down with seven holes to play, Poulter and Rose tried to make a miraculous comeback. Poulter birdied the 12th, then Rose the 13th. Poulter kept their hopes alive with a birdie at the 14th to cut it to 4-down with four holes to go.
Their hopes were dashed when Rose could only manage a par at the 15th and was halved by Jacquelin. The big win for Cejka and Jacquelin was the lone victory for the Continental European team, which lost 14 1/2 - 11 1/2 to the GB&I squad last year.
'You know we had a great start, Raphael birdied the first and I birdied the second,' said Cejka, the 2002 Trophe Lancme winner. 'It was good that we were 5-up after five holes.'
Despite the deficit, Ballesteros knows there is plenty of golf to play.
'I will go and speak to my players now, see what they feel like, how they feel about tomorrow and then I will make the decision on my pairings,' Ballesteros said. 'It was a tough day today but there is a long way still to go.'
Friday will see another set of fourball matches, before morning greensomes and afternoon foursomes on Saturday, and the traditional 10 singles matches on Sunday.