Westwood needs a victory at Valderrama to overtake Robert Karlsson for his second Order of Merit title. The fourth round was scheduled to be played in the afternoon.
Its in Lees hands and it has been for some time now, said Karlsson, who was 5 over for the tournament and trails Kjeldsen by 13.
Kjeldsen used three straight birdies on his way to a 69 for a three-day total of 8-under 205. The 86th-ranked Dane, looking to become the third wire-to-wire champion, led Sergio Garcia (70) and Westwood, with Englands Anthony Wall (71) at 4 under and Martin Kaymer (67) of Germany at 3 under.
Westwood, who needs the $899,000 winners check to take the title, drew even with Kjeldsen after a birdie at the long par-5 No. 11.
But Kjeldsen then let loose his string of birdies and Westwood bogeyed No. 12 to drop three shots back as the players completed the third round, which had been suspended Saturday due to heavy showers.
European money leader Karlsson, who could become the first Swede to lift the Harry Vardon trophy, continued to putt poorly on his way to a 72.
Karlsson leads Padraig Harrington by nearly $380,000 on the money list and Westwood by more than $594,000.
Harrington saw his Order of Merit chances drop after he could only manage a 71 for the second straight round and was at 5 over. The Irishman, who won the British Open and PGA Championship, needs a top-two finish to take the money title.
Miguel Angel Jimenez, already a long shot coming in, was 18 shots back of Kjeldsen with only a victory sufficient for the Spaniard to take the Order of Merit.