Cañizares set the target with a five under 66, but McIlroy, having bogeyed the fourth after finding sand, sank a 20 footer on the next and with a 15 foot putt at the sixth went into the joint lead.
Kaymer and England's Richard McEvoy were one behind and Dane Thomas Björn, winner of the marathon play-off at Gleneagles on Sunday, suddenly only two back when he rolled in a 35 foot eagle putt at the driveable seventh.
McIlroy, who lost a play-off in the event three years ago, said: "I took a lot of positives from that week and hopefully I can draw inspiration from it.
"My arm's nearly back to 100 per cent. I had a good bit of treatment on it and rested it.
"I kept my eye in last week, but it was nice to get back on the course and feel the competitive juices again."
Sunday's winner Thomas Björn was two over par after three, but hit back for a 68 - the obvious highlight of which was a 35 foot eagle putt after driving the par four seventh.
He was in joint fifth with Welshman Jamie Donaldson, England's David Lynn and Ryder Cup Swede Peter Hanson, while defending champion Miguel Angel Jiménez two further back after going out of bounds for a double-bogey six on the seventh.
Westwood made a start full of drama. He double-bogeyed the second, but played the next five in a remarkable six under.
After a birdie at the third he holed for eagle on the fifth, birdied the next and followed that with another eagle two at the seventh - like the fifth a driveable par four.
On four under he was up into joint fourth and there alongside him after a back nine 31 was compatriot Nick Dougherty, who last week suffered his 21st missed cut in a row.
Dougherty finished strongly at Gleneagles and, hugely encouraged by that, birdied the tenth, 15th, 16th and 18th.