The duo is knotted at 10-under-par 132, one shot clear of world No. 3 Phil Mickelson.
The three-time major winner, and co-leader after round one, shot a 3-under 68 on Friday at Loch Lomond. Mickelson is playing this week to prepare for next week's British Open Championship, but now has the benefit of trying to pick up some momentum with a win.
'I am looking forward to it' said Mickelson. 'It's going to be a lot of fun. I hit a few bad shots but I was able to keep it in play, make a few pars and a couple of birdies coming in.'
Mickelson was 1-under par after his opening nine, but he reached 8-under par for the championship thanks to a short birdie putt at the par-5 13th, a hole he eagled on Thursday.
He had a good look at birdie from 7 feet at the 15th, but missed, then found some trouble. Mickelson drove into the rough at 16, but saved par. He missed the putting surface at the par-3 17th and it was his vaunted short game to the rescue. The left-hander chipped to 3 feet and converted the birdie putt.
At the closing hole, Mickelson found the fairway off the tee, then stiffed his approach 7 feet from the hole. He sank the birdie putt to get within one of the lead.
'I was very fortunate to have shot under-par today,' said Mickelson. 'I wasn't hitting it where I wanted to. Hopefully I can get it turned around for the weekend to have a chance.'
Fellow American Boo Weekley (66), Simon Khan (67) and Andres Romero (67) share fourth place at 8-under-par 134.
Havret started well on Friday with two birdies in his first four holes. He parred the remaining five holes before the turn, then went on a run that vaulted him up the leaderboard.
He birdied four in a row from the 11th to move into the lead on his own at minus-9. Havret grabbed the clubhouse lead at 10-under par with a birdie at the par-4 16th.
Havret has played very well in recent weeks with a tie for 15th at the Open de France and a share of third last week at the European Open. He credited the turn in success to a belly putter.
'I went to my flat and was searching around and I saw the belly putter and said, 'oh, why not give it a try' because I was struggling a little bit on the greens. And since that my putting is a lot, lot better,' said Havret, whose only win on tour came at the 2001 Italian Open.
Lara did not start as well as his fellow co-leader; instead he birdied three out of four to close his front nine at Loch Lomond. He dropped a shot with a bogey at 10, but joined Havret in first with a spurt on the back nine.
He drained an 18-foot eagle putt at the 13th to get to minus-8. Heavy rain came into Loch Lomond, but the Spaniard collected back-to-back birdies at 15 and 16 to get into a share of first.
Lara has battled an Achilles injury all year and found the cure -- acupuncture.
'I had tried everything and was getting desperate. They said it was coming from my back and I had all sort of tests done but the only thing that made me feel better was the acupuncture,' said Lara, who picked up his only European Tour victory earlier this season at the Hong Kong Open.
Three-time major winner Ernie Els got back into the tournament on Friday. He shot a 5-under 66 and is tied for seventh place with Pelle Edberg (68), Miles Tunnicliff (67) and Steve Webster (67). The group is knotted at 7-under-par 135.
Mickelson's fellow first-round co-leaders struggled on Friday. Graeme Storm (72), Soren Hansen (73) and Lee Westwood (74) all plummeted out of the top 15.
U.S. Open champion Angel Cabrera posted a 1-under 70 in round two and made the cut on the number at 1-under-par 141.
Among those unfortunate players who will not be around on the weekend are: Retief Goosen (143), Trevor Immelman (143), Colin Montgomerie (143) and 2006 winner Johan Edfors (149).