The Swede started slowly with bogeys on the third and fourth but made a birdie on the sixth and then six in seven holes from the eighth, with an 18-footer on the 14th getting him to five under and into share of the lead.
He dropped a shot on the 16th to fall back into second but was still left to reflect on a very satisfying day's work at a wild and windy Walton Heath Golf Club.
“I think I was hitting it all over the place the first four,” he said. “The first four holes are really tough as well but from there it was really good.
“I was kind of wide off the tee the first few holes there and then I just found the middle after that. You get a lot of chances on this course if you're on the fairway.
It's really nice to be back playing good golf - Joakim Lagergren
“It hasn't been great lately, unfortunately. I've been struggling lately with my swing. I couldn't really see this coming, either, you never know when it's going to come. That's just golf, I guess, but it's really nice to be back playing good golf.”
Lagergren beat Mike Lorenzo-Vera in a play-off to win his first European Tour title earlier this year at the Rocco Forte Sicilian Open and the Frenchman was alongside him at four under after picking up five shots in his final eight holes.
“I'm really happy,” said Lorenzo-Vera. “It was tough out here, hard to hit the fairways with those crossing winds and dry grounds.
“If you start missing the fairways, you're chipping a bit far from the hole and then these greens are really fast. It can be brutal.”
David Lipsky made a flying start with four birdies in his first five holes but after a run of seven pars, he dropped shots on the fourth and sixth to fall back.
A strong fightback saw the American birdie the seventh and eighth and he will also head into day two at four under.
“I played great,” he said. “It was tough out there, it was really tough with that wind and the rain started coming down, the fairways are really firm. I played really well today, really happy with it.
“I've been playing terrible so to get this round going really helps me. I'm looking forward to the rest of the week. I've figured some stuff out so I'm pretty excited.”
Englishman Richard McEvoy completed the group in the clubhouse one off the lead after making six birdies and two bogeys and he was loving making a rare appearance on home soil.
“I haven't done it for a long time,” he said. “I think Wentworth probably five or six years ago was probably my last time I've actually played in front of English crowds in particular.
"So yeah, lovely to have some support and some people here following me. Hopefully another good day tomorrow and be in a good position for the weekend.”