Rafael Cabrera-Bello shot a brilliant round of 64 to lead the Portugal Masters by one shot heading into Sunday's final day in Vilamoura.
The Spaniard picked up five birdies, two eagles and one bogey to finish 18 under par, one ahead of Sweden's Christian Nilsson (66) and Chile's Felipe Aguilar (67).
The 27-year-old, who won the Austrian Open in 2009 with a closing round of 60, said: "It felt really good, I've been playing good the last few days.
"My goal today was to try and do the same thing. The two eagles definitely gave me a big boost and I think I played pretty solid.
"I did not make many mistakes. I've been hitting my irons really good this week, hitting them close and giving myself lots of opportunities and I've been able to make a few. Hopefully I can keep it up tomorrow."
Cabrera-Bello added on Sky Sports 1: "I probably won't be leading tomorrow by the time I tee off so I need to perform well and try to hit a low round again."
Sweden's Peter Hanson and Denmark's Thomas Bjorn are just two shots off the lead on 16 under, Hanson carding a superb 64 and Bjorn - seeking his fourth win of the season - returning a 66.
Hanson, a member of the victorious Ryder Cup team at Celtic Manor last year, said: "I wasn't really thinking about a 64 but I got off to a good start and managed to keep a bit of momentum into the back nine.
"I've been struggling a bit with every part of my game this season, it has not been consistent but I've been working hard on that the least few weeks.
"I'm just outside top 15 on the Race to Dubai and would love to get into that. I'm also 51st on the world rankings and it would be nice to move up there as well."
South African Hennie Otto was among those on 14 under after producing a brilliant 63.
Otto carded seven birdies and an eagle to complete his round two hours before overnight leader Simon Khan was due to tee off.
The 35-year-old made the cut with nothing to spare on five under after rounds of 72 and 67.
"I got it to six under yesterday with three holes to go and then I double-bogeyed the seventh," Otto said on www.europeantour.com.
"I had five under par in my head to be the number for the cut and I chipped and putted on the eighth for par but then managed to birdie nine to get in right on the mark.
"With the early time and fresh greens, I really wanted to have a go. I played well last week but made 18 pars in a row in the first round.
"Yesterday I also played well but didn't make the putts, but I knew it was going to happen sooner rather than later for me."