Open champion Shane Lowry and world No 20 Matt Fitzpatrick share the lead in the $7 million Rolex Series events after impressive matching efforts of 67-65 so far to sit on 12-under-par, one ahead of Tyrrell Hatton after the double Dunhill Links winner backed up an opening 66 with a 67.
Dundee-based Frenchman Victor Perez and Dane Joachim B Hansen are tied for fourth on nine-under, with Forrest’s splendid work so far leaving him alongside Spaniard Adri Arnaus on eight-under heading into the weekend at the Surrey venue.
The 27-year-old Scot, who played the iconic course for the first time on Tuesday, backed up his first-day 69 with a 67, which was a brilliant effort considering it included a lost ball.
"Really pleased and really happy," said Forrest of his performance so far in the tour’s flagship event and his position at the halfway stage.
Starting at the ninth, he followed an opening par with three straight birdies before adding another three birdies in four holes to be six-under for the day and nine-under overall after nine holes.
That lost ball off the tee at the 18th - his tenth - led to a bogey-6, though the fact he holed from around 20 feet to stop the damage from that being greater was a huge moment in the round as he then added eight pars to finish.
"The first eight holes, I played excellent, didn't really miss a shot," said the Lothians man afterwards. "The lost a ball on 18, where I hit it right off the tee, was the only real blip. I did well to make birdie on the second one. That kept the momentum going into the last eight holes.
"It was a little bit scrappy on the last few holes, losing my rhythm a little bit coming in there, but I managed to hole out really well."
Forrest is chasing his maiden win on the European Tour and, even though he graduated to the top circuit without tasting victory on the Challenge Tour, he is relishing the challenge over the final 36 holes.
"The Challenge Tour prepares you so well for coming out here,” said the former Scottish Amateur champion. “All of the events are a lot stronger fields and you just try to put yourself in position for the weekend.
"This course is just about hitting quality golf shots. You just have to hit good shots. We've had quite a lot of wind the first day and a half and you just really need to be in control of the ball."
Lowry, who made a late decision to play in this event after skipping last week's Scottish Open having supported the Irish Open the previous week, was runner up in this event in 2014 and has recorded three other top-10 finishes.
"I wasn't too sure whether I was going to play or not," he admitted after signing for a bogey-free seven-under second effort. "On Monday, I seen this putter sitting there and I put it down and had a look and was like, 'well, I'll bring it for the spin'.
"I went to play nine holes with my coach (Edinburgh man Neil Manchip) on Monday evening at The K Club and putted quite nicely, so brought it and it's definitely worked so far as I've been struggling on the greens."
Fitzpatrick, a five-time European Tour winner, was on course to beat Paul McGinley's record halfway total of 13-under-par, set in 2008, after making an eagle and seven birdies in 17 holes before finishing with a double-bogey 6.
"Drove the ball well. Chipped well. Putted well. Iron play is good," he said in shaking off that blip. "I feel the last few weeks I've done three things well and one thing's been off. It's nice for it all to come together.
"This is my best position I've been here. I love the golf course. I've always felt it suited my game. Never really kicked on around here, but if I can just keep playing how I've been playing, make some putts as well, there's no reason why I can't finish it off."
Perez, who landed his first European Tour title with victory in the Alfred Dunhill Links Championship this time last year, is in the hunt for another big win after making an eagle and five birdies in a 66.
"I don't know if it's coincidence," he said of his habit of hitting top form in the autumn. "Every year so far I've been getting to a new level playing better tournaments, bigger tournaments.
"I think it's taken me a couple of months through the middle of the year to adapt and get comfortable, but I'm obviously pleased to play well towards the end of the season. But there's plenty on my plate (here)."
Scottish No 1 Bob MacIntyre came home in 34, three-under, for a 68 to sit in a tie for 30th on three-under, while Richie Ramsay (71) and Stephen Gallacher (71) also made the cut on two-under and one-under respectively.
David Howell's hole-in-one at the 14th courtesy of a 7-iron from 184 yards resulted in £71,675.01 - the value of a sponsor's car on display - being donated to Alzheimers Society.