The Australian golfer shook off a pair of bogeys down the stretch to make par on the 18th hole, while Clarke, who was tied with Lonard heading to the final hole, posted his third double-bogey of Sunday's final round to finish in a five-way tie for second.
"It's something you wonder if you'll ever get to, to win, and it's a great feeling," said Lonard after shooting a four-over-par 75 in the final round of the MCI Heritage on Hilton Head Island, S.C.
Lonard opened the tournament with a 62 at Harbour Town Golf Links but lost the lead after a shaky second round. He battled back to secure a one-shot lead over Clarke with one round to play.
Peter Lonard holds the trophy after winning the MCI Heritage Sunday at Harbour Town Golf Links on Hilton Head Island, S.C. (AP Photo/Mary Ann Chastain)
Lonard hit a solid drive at the 18th on Sunday and knocked his second shot to 18 feet. Clarke then gave the tournament away when his approach to the 18th missed badly to the left and found the thatch.
Clarke took a drop and walked away with another double-bogey while Lonard posted his first win on the U.S. circuit with a seven-under 277.
Clarke shot 76 on Sunday and joined Jim Furyk, Billy Andrade and Davis Love III at five-under-par 279. He held a six-stroke advantage after 36 holes.
Calgary's Stephen Ames, Rod Pampling and Thomas Levet tied for sixth place at four-under 280.
Lonard found himself trailing Clarke by four strokes on the front nine in Sunday's round.
Clarke ran off three consecutive birdies while Lonard bogeyed each of his first two holes. Clarke drained a five-foot putt for a birdie at the fifth but Lonard managed to keep pace with a birdie of his own at the very same hole.
At the par-4 sixth, Clarke hit his tee shot into a bunker and hit out to eight feet. He missed the par putt and dropped another shot at the par-3 seventh. Lonard then hit his tee shot to 20 feet and converted the birdie try at the seventh to move within one of Clarke at 11-under.
"I got off to a great start, thought everything was going well, and just started making some bad swings, and it went from bad to worse, and I seemed to be fighting that hook all day," said Clarke.
Clarke's problems continued at the par-4 eighth where he hit his drive into the water en route to a double-bogey and just like that Lonard was back in the lead.
Lonard wasn't out of the woods, however, and dropped a shot at the ninth to join Clarke in a tie atop the leaderboard.
"I hung around the mark, and he made a couple mistakes, which isn't that hard to do here," said Lonard. "The birdies were hard to come by, the wind was a bit fluky, the greens were really tricky, so I was trying to hit greens in regulation and give myself a lot of opportunities."
Clarke played his approach to 16 feet for a birdie at the par-4 12th to take a two-shot lead while Lonard bogeyed the hole.
Clarke made a mess of the par-4 13th, however, for another double-bogey and the wheels kept coming off as the 36-year-old bogeyed each of his next two holes two fall back to seven-under.
with files from Sports Network
