Both are bidding for their first European Tour title.
Lagergren (66) had eight birdies and two bogeys for a 6 under in Friday's second round.
He is joined at the top of the leaderboard by Frenchman Joel Stalter after the 24-year-old signed for a four-under-par 68, a round that included six birdies and two bogeys.
Garcia had held a share of the lead at the turn after a hat-trick of birdies from the seventh, but dropped shots on the 14th and 17th stalled his momentum before he carded a closing birdie in a round of 70.
Ronaldo header gives Portugal win at Confederations Cup
He peaked from April onward with a rush of Champions League goals, including two in the final to help beat Juventus 4-1. However, goals from Raul Jimenez and Oribe Peralta sealed the three points for Mexico and sent them top of Group A .
"It was great out there", Lagergren told www.europeantour.com.
"I felt like I played quite well, not spectacular, but very consistent", Garcia said. Just a couple little mistakes here and there. "You don't have to be ashamed of three under I guess around here".
Stenson, the defending champion, went one better with a 69 as he joined Garcia, Richard Bland, Rikard Karlberg and Thomas Detry at 8-under.
"I'm in a good position", said Bland. "I'll keep doing the job here and hitting good shots, making putts, and we'll see where I stand on Sunday".
Stenson sat just one shot back after two rounds, courtesy of a round of three-under that featured just a single blemish.
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