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On the first, Kaymer almost holed his second shot but a tap-in birdie was enough to take an early lead, and it only got better for the European pairing as they opened up a three-shot advantage after four holes.
Fowler struck back with a birdie on the fifth, but Kaymer squandered a chance on six to regain the three-shot lead.
The seventh and eighth were shared and the ninth looked to be heading the same way before Walker produced a stunning shot from the bunker to hole out for an eagle to halve the deficit at the turn.
Keep track of the back nine by following Sports Mole's live text coverage.