The convincing win, much like his wire-to-wire victory in the Derby two weeks ago, sets up trainer Bob Baffert for his third shot at a Triple Crown in the last six years.
Baffert's Silver Charm in 1997 and Real Quiet in 1998 both won the Derby and Preakness but fell short in the Belmont.
War Emblem, who held off fast-closing long shot Magic Weisner by three-quarters of a length, didn't show up in Baffert's barn until three weeks before the Derby, when the colt was bought for $900,000 by Saudi Prince Ahmed bin Salman.
On June 8, War Emblem will attempt to become the first Triple Crown winner since Affirmed in 1978 and the 12th horse to sweep the Derby, Preakness and Belmont.
Baffert, who was out of Triple Crown options before War Emblem showed up, has now won four straight Triple Crown races and eight of the last 17.
The greatly anticipated showdown at the start with speedsters such as Booklet and Table Limit failed to materialize. Instead, long shot Menacing Dennis shot to the front and held the lead. War Emblem, with Victor Espinoza aboard, was second just off the pace.
When the field of 13 3 year-olds turned for home, War Emblem moved into the lead by two lengths and began to widen his advantage.
Proud Citizen, trained by D. Wayne Lukas, looked to have second place wrapped up, but local favorite Magic Weisner — a 45-1 shot — made a late rush to finish second.
War Emblem covered the 1 3-16th-mile Preakness in a slow 1:56.36.
Sent off as the 5-2 favorite, War Emblem returned $7.60, $6 and $4.40. Magic Weisner, with Richard Migliore aboard, paid $33 and $14. Proud Citizen, ridden by Mike Smith, was third and returned $5.
"It's a shame we ran out of racetrack,'' Migliore said in what could have been the biggest upset in Preakness history. ``He was getting to him really quick."
But like the Derby, nobody could catch War Emblem, who becomes the eighth horse to try for a Triple Crown since Affirmed won his 24 years ago.
After the race, the ornery, nearly black colt still had enough energy left to try to nip the outrider pony who was escorting him to the winner's circle.
Straight Gin, trained by Nick Zito and ridden by Robby Albarado, was ninth and was taken from the track by ambulance with a non life-threatening bowed tendon.