Joe Durant actually birdied the longer 18th at the Blue Course at Doral Resort and Spa to shoot a 6-under 66.
The hole was lengthened from the tee, making the drive very difficult with water on the left. There were some other minor alterations in length and swirling winds made Thursday's opening round difficult.
Phil Mickelson, Scott Verplank and 2001 U.S. Open champion Retief Goosen each posted rounds of 5-under-par 67 to share third place.
Smith reached the par-4 18th at 9-under par and ripped his drive down the center of the fairway. He had a 5-iron into the green, one of the smallest clubs hit at the hole during the round, but the wind pushed it left into the water.
After a drop, Smith hit a wedge 35 feet over the hole with his fourth. His bogey putt never came close to the hole, but the 2002 Buick Classic champion still took the first-round lead for the first time since the Memorial three years ago.
'It is a hard shot to begin with,' said Smith, referring to No. 18. 'I felt like I had plenty of club and I hit a lot of good shots all day. I came over it just a little bit and the wind grabbed it, went in the water and I made six.
'It's alright. I made one marginal swing on the last hole and hopefully I'll feel good again tomorrow morning.'
Before Smith fumbled the 18th hole, he flew out to 10-under during the first round.
Smith was 4-under par through his first five holes with an eagle at one and birdies at three and five. He birdied the par-5 eighth hole, then added a 25-footer for birdie at the ninth to make the turn at 6-under-par 30.
Smith continued his birdie run at the 10th to make it three in a row and the 34-year-old made it four straight at No. 11 when he knocked a 6-iron on the fringe 10 feet from the hole.
At the par-5 12th, Smith came up short with his second shot and pitched his third 15 feet past the hole. He drained the birdie putt and knocked his tee ball to five feet at the par-3 13th to set up his sixth birdie in a row and grab a five-stroke lead.
'It snowballed into a little bit of confidence,' said Smith. 'It was fun.'
It stopped being fun at the 15th when his eight-footer for birdie died right. At No. 16, Smith drove into a bunker on the left side of the fairway and flew his second long and left of the green. His pitch rolled through the green 30 feet from the hole and he missed the par save.
Despite the mishaps late Thursday, this was Smith's best of the round of the season by three shots over last week's 68 in the opening round of the Chrysler Classic of Tucson.
'I think overall it's the best round I've played this year,' said Smith. 'I got the putter rolling at the start of the round and I made some putts. I drove it pretty good and I hit some good iron shots. Everything kind of came together.'
Durant, the 2001 champion, tallied three birdies in his first four holes but went dry from there. He recorded one bogey and seven pars over his next eight holes then went on another birdie run.
He collected three birdies in a row from the 13th and made a clutch par save at the 17th. Durant ran home a seven-foot birdie putt at the closing hole to get within one of Smith, a feat that looked pretty impossible about an hour earlier.
'The putter's been pretty dry the last two years, but I made some changes in the off-season and I'm starting to see some results,' said Durant, who won twice in 2001 but has only four top-10s since.
Chris DiMarco, Mark Calcavecchia, Briny Baird, Tim Clark, Zach Johnson, Craig Perks, Todd Hamilton, Dennis Paulson and John Riegger share sixth place at 4-under-par 68.
Defending champion Scott Hoch posted a 2-under-par 70 and is part of a group tied for 19th place.
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