(CNN) -- Unfancied German Marcel Siem will take a three-shot lead into the final round of the Wales Open on Sunday as he seeks his second European Tour title.
The 29-year-old, who has dropped to 294th in the world rankings since his only previous success at the 2004 Dunhill Championship, carded five-under-par 66 in his third round on a day of low scoring at Celtic Manor.
Joint halfway leader Siem, who won the World Cup teams event with Bernhard Langer in 2006, followed up his opening rounds of 69 and 67 as he fired five birdies in a flawless 18 holes.
He will be chased by former Ryder Cup star Thomas Bjorn, who has dropped to 215th in the rankings, after the Dane shot 68 to be tied for second with Spain's Gonzalo Fernandez-Castano.
While the Spaniard matched Siem's 66, a trio of British players tied for fourth another shot back on seven-under 206 did even better.
Scotsman Stephen Gallacher broke the course record with a 63 that featured six birdies and an eagle at his final hole, while Northern Irishman Graeme McDowell fired an eight-birdie 64 marred by a bogey at 16 and England's Simon Dyson shot 65.
Gallacher, the nephew of former Ryder Cup Captain Bernard, is rebuilding his career after having to go to qualifying school last November following a serious viral infection.
He finished fourth at the BMW Championship two weeks ago which pushed him up to 28th in the Race To Dubai money list.
"I've been knackered, but I've just got a wee bit of belief in myself," he told reporters.
"There's no point not enjoying being in that situation tomorrow, but what the golf is going to be like, you never know."
Fernandez-Castano, a four-time European Tour winner, is seeking his first victory since the 2008 British Masters.
"I have been putting nicely over the last couple of days and today it was okay," he said. "I am quite confident since I got rid of the belly putter.
"I have been putting a little better even though I know I am moving over the ball and my technique is terrible, but the ball is going into the hole and that is all that I am interested in."
Celtic Manor will be the host venue for the Ryder Cup in October as the European team seek to regain the title from the United States.
Europe captain Colin Montgomerie's Wales Open title hopes were dented as he slumped from equal 14th to a tie for 47th following a 76 that featured three bogeys and two doubles.
Australia's Andrew Dodt, who had shared the halfway lead, dropped to a tie for 21st as he also carded two double-bogeys in his 75.