Rory McIlroy remained in contention for a second Dubai Duty Free Irish Open title, in spite of experiencing more frustration at Ballyliffin.
McIlroy was delighted with his long game in an opening round of 70 on Thursday, but struggled on the greens and let a number of birdie chances go begging in the £5.3million event, part of the European Tour's lucrative Rolex Series.
And the four-time major winner suffered more of the same in the early stages of the second round, starting from the 10th with six pars in succession before dropping a shot on the 16th after finding a fairway bunker, despite taking an iron off the tee.
A two-putt birdie on the par-five 17th got McIlroy back to level par for the day and two under overall, just three shots off the lead shared by Danny Willett, Ryan Fox, Peter Uihlein and Joakim Lagergren.
Willett reached a career-high of ninth in the world after his victory at Augusta National in 2016, but has slumped to 442nd in the rankings after suffering numerous injuries and a loss of form.
A missed cut in last week's French Open was his ninth in 12 events this season, but after an opening 68 at Ballyliffin the 30-year-old picked up two birdies in his first nine holes on Friday to improve to six under par.
That was briefly enough for the outright lead until Lagergren, who won his first European Tour title in Sicily in May, birdied the 13th and 14th to move to the top of the leaderboard.
McIlroy saw a short birdie putt on the 18th horseshoe around the hole and he remained two under par with six holes remaining.
McIlroy, who won this title in 2016 but has missed the cut in four of the last five years, could not convert from 12 feet for eagle on the par-five fourth and quickly handed back the shot gained on the next after needing two attempts to escape a greenside bunker.
However, the 29-year-old bounced straight back with a birdie on the sixth after a superb approach and at three under par was just four behind joint leaders Lagergren and Willett.
Ryder Cup vice-captain Lee Westwood was two shots off the pace after recovering from dropping three shots in the space of four holes with birdies on the fourth and fifth.
McIlroy's patience was being sorely tested and his mood was not improved by dropped shots on the eighth and ninth to complete a disappointing 73 which left him six shots behind clubhouse leader Lagergren.
Willett's bid for a first win since his Masters triumph suffered a blow when he followed McIlroy in needing two shots to escape from sand on the fifth, but birdies on the sixth and ninth left him six under par and just a shot off the lead.
That could result in an England-Sweden pairing with Lagergren in the third round while the respective countries contest a World Cup quarter-final in Russia.
"It's a nice problem to have but I'm sure the crowd will let us know the score, especially if England are losing!" Willett joked.
The biggest threat to Lagergren's lead appeared to be South Africa's Erik van Rooyen, who had stormed to the turn in just 30 shots thanks to a birdie at the first and four more in the space of five holes.
That took Van Rooyen to six under par alongside first-round leader Ryan Fox and France's Matthieu Pavon, who had four and nine holes to play respectively.
The halfway cut was projected to fall at one over par and defending champion Jon Rahm had successfully moved inside that mark, the world number five following an opening 74 with two birdies in 12 holes on day two.
Van Rooyen's charge was slowed by a bogey on the 11th and it fell to Fox to finally overhaul Lagergren, birdies on the 16th and 18th giving the Kiwi a second round of 69 and a halfway total of eight under par.
Pavon had reached the same mark with an eagle from 15 feet on the fourth and, after dropping a shot on the sixth, bounced straight back with a birdie on the seventh.
England's Sam Horsfield, a protege of Ryder Cup star Ian Poulter, had moved to seven under thanks to birdies on the third and fourth.