Angel Cabrera, the 2007 U.S. Open champion, was third with a 65 in this tuneup before the British Open at Royal Birkdale, which begins July 17.
Mickelson and Els both returned from three-week layoffs. Mickelson had a 71 and Els was at 1-over 72.
The golf course was ideal for scoring, soft with lift, clean and place. I just didnt get the ball in the hole, Mickelson said. I thought I hit a lot of good shots but I didnt capitalize with my putts and let a good round slide a little bit.
If I go out tomorrow and have a good round, I should be able to get right back in it for the weekend.
Els said, I played some good stuff and some bad stuff. I had a bad shot on four, made double then a bogey on five. Then I played well but lipped out for birdie on 15 to get to 2 under.
Jaidee of Thailand and Noren of Sweden thrived on the course at Loch Lomond, and played well even with a rain delay.
Thongchai made four straight birdies on the front nine, then birdied the last two holes after overnight rain delayed the start of play by 90 minutes.
Noren finished with a bogey-free first round.
Ive had too many high scores, too many double and triple bogeys so having no bogeys was great, he said.
Niclas Fasth, Garry Houston and John Bickerton were at 66.
Colin Montgomerie, the 1999 champion, shot 69 after bogeys on two of his final three holes.
Third-ranked Adam Scott, playing with a hand injury, had a triple bogey 7 on his first hole on the way to a 72.