McDowell and McIlroy picked up seven birdies in their first 11 holes Saturday of fourball competition en route to the 64. They are at 21-under 195 after 54 holes.
Germans Alex Cejka and Martin Kaymer and South Africans Louis Oosthuizen and Charl Schwartzel each shot 11-under 61 while the U.S. team of Matt Kuchar and Gary Woodland had a 63 Saturday. Those three teams are tied for second at 19-under.
Australia -- the team of Richard Green and Brendan Jones -- led after the first round and was tied with Ireland after Friday's play but had a 5-under 67 Saturday, slipping to fifth place at 18-under. The Netherlands is 17-under and defending champion Italy and Mexico are tied for seventh, five strokes behind McDowell and McIlroy.
Ireland was the pre-tournament favorite and lived up to that Saturday. McDowell and McIlroy had birdies at Nos. 2 and 3 and then three in a row from 5-7. They opened the second nine Saturday with birdies at 10 and 11 and got to 8-under on the round with another at 16.
The tournament includes two rounds of fourball and two of foursomes alternately shot for each team. Sunday's round will be foursomes. McDowell and McIlroy tied for the best round in Friday's foursomes format.