Padraig Harrington stormed into contention at the Portugal Masters as a brilliant round of 63 left the Irishman just one shot off the halfway lead.
The Dubliner began the day three shots off the lead at five under par, and low scores were again the order of the day in Vilamoura.
Scot Marc Warren was among the early starters and looked set to add to his overnight lead with a round of 65 that saw him reach the 36-hole mark at 14 under.
But the birdies continued to rain down at Victoria Clube de Golfe, with defending champion Andy Sullivan firing a bogey-free round of 61 to join Warren at the top of the leaderboard.
Harrington is just one stroke back - alongside Swede Jens Fahrbring - after shooting nine birdies in his second round.
The 45-year-old's last European Tour win came courtesy of his 2008 US PGA Championship triumph, but he opened with four birdies in his first five holes and rebounded from his lone dropped shot at the par-five 12th with a total of five birdies coming home.
Sullivan, who could move into the top 50 of the world rankings with a strong showing this week, was not the only player to record a 61 on Friday.
Scot Richie Ramsey had earlier achieved that feat in a round that included 11 birdies and a single bogey on the 16th, leaving him four shots adrift of the leaders.
The two 10-under scores equal the lowest round of the season on the European Tour, matching Tyrrell Hatton's 62 at St Andrews at the Alfred Dunhill Links Championship.
Paul Dunne missed the cut despite shooting a second-round 67, and now faces a nervous wait to learn if he will retain his European Tour card for 2017 beyond this weekend's cut-off point, while Michael Hoey also failed to make the weekend.
