The top-ranked Donald and McIlroy have been swapping the No. 1 ranking this spring. Westwood, currently No. 3, is a former No. 1 who is leading the European Tour stop in Sweden this week.
McIlroy won the 2011 U.S. Open by eight strokes but has missed the cuts in his last three starts.
The threesome will tee off at 4:29 p.m. EDT Thursday on the first hole. Their second round is to start 10:44 a.m. Friday at No. 9 of The Olympic Club in San Francisco.
Perhaps an even more attention-grabbing group will be Tiger Woods, Phil Mickelson and Bubba Watson. They have 19 major championships among them, with Watson chipping in the 2012 Masters title. Woods has three U.S. Opens among his 14 major tournament championships. Mickelson hasn't won the Open but has finished second five times.
They are to tee off on the ninth hole at 10:33 a.m. EDT Thursday and from No. 1 at 4:18 p.m. EDT Friday.
Three young U.S. players -- 2011 FedExCup winner Bill Haas,. Nick Watney and Brandt Snedeker -- will also be together the first two rounds.