Andalucia Masters second round leaderboard:
-7 G McDowell (NI) -5 G Maybin (NI) -3 N Fasth (Swe) -2 MA Jimenez (Sp) G Boyd (Sco)
Selected others:-1 D McGrane (Ire) level D Clarke (NI) +2 R Fisher +3 JM Olazabal (Sp) +4 M Kaymer (Ger) +7 P McGinley (Ire)
Kaymer has won his last three events including the USPGA Championship
Martin Kaymer's bid to become world number one looks destined to end in failure after a disappointing second round at the Andalucia Masters.
The German, who needs to finish in the top two to usurp Tiger Woods, struck a 75 to slip to four over par, 11 shots off Graeme McDowell's Valderrama lead.
Should Kaymer not finish in the top two the absent Lee Westwood, resting a calf injury, would replace Woods at the top.
Northern Ireland's McDowell hit a fine 67 to move to seven under par.
And with half a million euros on offer to the winner this week, McDowell is on course to close the gap on Kaymer in the Race to Dubai, the European Tour money list.
Kaymer, 25, currently leads US Open champion McDowell by almost a million euros.
Kaymer, winner of his previous three events, was one under for his round after chipping in for a second birdie of the day on the seventh, but then dropped shots at the ninth, 14th, 16th and 18th after missing a three-foot putt.
McDowell, who secured the winning point for Europe in the Ryder Cup at Celtic Manor earlier this month, struck four birdies on the back nine to surge two shots clear of his fellow Northern Irishman Gareth Maybin.
"Martin has not had the best two days out," McDowell said. "He is a world-class player and I fully expect him to have a good weekend but the forecast is for the wind to get up which could make low scoring difficult."
Sweden's Niclas Fasth, seeking a first European Tour title since 2007, is a further two shots back after a 66.
"I am very pleased and somewhat surprised because my game is not so solid, but my putting and my short game were sensational," said Fasth.
"On this course you need to have a good short game even if you are in great form. I have had another tough season this year, but it's getting better at the end and here I have found a bit of spark, a bit of energy."
Overnight leader Pablo Larrazabal of Spain slipped out of contention after following his opening day 66 with a six-over-par 77.