The win meant Kaymer will pick up enough points to slip past the current No. 1 player, Lee Westwood, who was eliminated in the second round.
"It is a very proud moment for me, my family, all the people who helped me, and Germany, as well," he said. "To be the second one to do it is a nice feeling."
Bernhard Langer was the first German to reach No. 1.
Kaymer has reached the top with an impressive mix of power and precision. He's reasonably long off the tee, accurate with his irons and an outstanding putter. That combination was too much for Watson, who rallied from 5 down with eight holes to play to knock out J.B. Holmes in the quarterfinals.
Watson's semifinal match against Kaymer was all square with four holes to play. At the drivable par-4 15th hole, however, Watson sliced his shot left of the green into desert scrub and was forced to take a penalty drop. Kaymer got up-and-down from a bunker for birdie and a 1 up lead. At the par-3 16th, a gust of wind caught Watson's tee shot and sent it long, just over the green. Watson failed to get up-and-down and went 2 down after Kaymer made par.
But Watson fought back with a clutch six-foot birdie putt on No. 17 to keep the match alive. On 18, Watson's run ended when the hole was halved with pars. Kaymer advanced to the final match — and earned the No. 1 ranking.
One question, though: Why are world ranking points even awarded for the Match Play Championship? A player who wins this week only has to beat six opponents instead of 155, like a regular stroke-play event.