By Bernie McGuire
Westwood troubled by a calf problem during the tournament said he planned to take about a month off in order to let the injured muscle fully heal.
Defending champion Simon Dyson closed with a 66 and a share of fifth place.
"It was always one of my dreams to win here at St. Andrews," Kaymer told reporters.
" I can still remember my first day I came out here when I was an amateur and walking down the first hole, walking over the bridge, all of those things, they felt very special to me.
"So it was very, very special for me to win here today, in the Home of Golf."
England's Willett moved to 19th on the Race to Dubai money list by finishing second on 14-under par. The 23-year old eagled the par-five 14th on route to a final-round 67.