Jamieson followed a bogey on the first with a double bogey on the third, but birdied seven of the next nine holes – including four in a row from the ninth – to add a 70 to his opening 67 at Wentworth.
That left the 33-year-old from Glasgow on seven under par alongside Belgium’s Thomas Pieters and Italy’s Francesco Molinari on top of a crowded leaderboard, with Germany’s Max Kieffer a shot behind.
Open champion Henrik Stenson, Lee Westwood, Branden Grace and 2015 winner Byeong Hun An were a shot further back on five under, while Masters runner-up Justin Rose eagled the last to make the cut.
Jamieson narrowly retained his card in each of the last two seasons by finishing 106th and 107th on the Race to Dubai, but can afford to focus on securing a second European Tour title after two top-four finishes in 2017.
“This would be up there with the Scottish Open,” Jamieson said. “I’m not in any of the majors this year so this is as big as it gets. This is the pinnacle of my season.
“It’s huge, it’s our flagship event. It would start opening up doors that have been closed for a few years. You want to challenge yourself against the world’s best and we don’t get to do that every week, but we do this week. Hopefully I can take a few of them down.”
Speaking about his round, Jamieson added: “I’m delighted, especially with the way it started.
“My ball was plugged in a bunker on the third and I thought it would take a good shot to get it on the green. Then I didn’t get up and down and at that point I would have bitten someone’s hand off for around level par.
“The last thing you need to do is panic. There are birdies out there if you hit some good shots and I’ve been playing well. Making birdies is something I’ve always thrived on. That’s where you get the buzz.”
The £5million renovation of the West Course has helped persuade Stenson to make just his second appearance in the event since 2010, a stark contrast to Westwood’s 24th visit in succession.
“It’s nice to play a golf course where you’ve got to use your brain,” said Westwood, who was second in 2000 and 2011. “I’ve played patient and sensible golf and approached it a bit like a major – playing away from certain pins, taking irons off some tees.
“It’s hurting golf going to courses that are 7,600 yards, where the caddies can just hand you the driver on every hole and walk forward.
“I like the way the course is set up this week, nobody can have any excuses. The course is really fair and consistent, you don’t get too many bad lies or bounces. For a few years it drove people mad.
“I’ve played well here in the past and had a couple of chances and just need to finish it off.”
Ian Poulter labelled his putting “pathetic” despite a 69 which was a seven-shot improvement on his opening round, the 41-year-old carding 16 pars, one birdie and an eagle on the 12th to finish one over par.
That was a total matched by former Masters champion Danny Willett after a 73, while Rose and defending champion Chris Wood finished a shot further back.
Rose looked set to miss the cut after shanking a fairway bunker shot out of bounds on the sixth to run up a quadruple-bogey, but produced a grandstand finish with an eagle from 10 feet on the par-five 18th.