Coltart fired a round of 69 Saturday at De Vere Slaley Hall to move to 11-under-par 205. He is most closely trailed by Bradley Dredge (72) and Jamie Spence (70), while five others are four shots back at minus-seven.
Coltart opened his round in strong fashion, crafting birdies at Nos. 4, 5 and 7 to be out in 3-under 33.
Another birdie at the par-5 11th saw him move to 12-under for a time, but was negated with a bogey at the 15th.
Im very happy that I got the job done out there today and hopefully I can do a similar job on Sunday, stated Coltart, who is searching for his second win on the European Tour.
There are a lot of guys capable of shooting great scores but I would be disappointed not to win, thats only natural.
Spence could more than likely be the one to shoot a low number on Sunday, as the 38-year-old Englishman has posted a 60 on the European Tour once before. In addition, he closed in 64 during his last win at the 2000 Moroccan Open, in which he came from three back.
Dredge might also make a run at his first win on the tour, but he says he first needs to find better luck on the greens of Slaley Hall.
I was disappointed as I didnt putt as well, didnt attack the hole, Dredge said. I was happy with my ball striking and will focus on attacking the hole on Sunday.
The recently-turned 28-year-old may have been referring to the long iron second shot he played to the par-5 4th, which he converted from 15 feet for eagle.
The score saw him jump into a temporary tie for the lead with Coltart, but he was not able to sustain his good play.
A final bogey at No. 15 saw him drop to three back.
Should Coltart hold on for victory Sunday, it would mark the 30-year-olds first win since the 1998 Qatar Masters.
Full-field scores from the Great North Open