Damien McGrane and Luke Goddard retained the lead of the Estoril Open de Portugal after solid starts to their second rounds.
But Englishman Steve Webster surged to within one stroke of the pair's 11-under-par total after four successive birdies around the turn.
Starting from the 10th hole, Webster birdied the 12th and picked up a further shot at the 18th.
That sparked a birdie streak as he embarked on the front nine with three successive threes to move to five-under for his round and 10-under overall.
Compatriot Goddard had finished with four birdies yesterday for a 64 and added four more on the front nine today, though a dropped shot at the par-three fifth left him level with McGrane at the turn.
The Irishman - like Webster, starting on the back nine - birdied his second and third holes of the day before bogeying the par-four 14th.
He picked up further shots on the second and third however for a share of the lead with 12 holes played.
Australian Andrew Tampion also profited from the friendly front nine, four birdies compensating after he played the back nine in one over par and leaving him a shot behind Webster and level with Spaniard Carlos del Moral, who birdied five of seven holes around the turn.