The Bexhill-based star won five matches to reach the semi-finals of Players Tour Championship event seven at the South West Snooker Academy near Gloucester.
Robertson, who went into the event ranked 57th in the world, saw off world no.79 Paul Davison 4-1 in round one before knocking out six-times World Championship runner-up Jimmy White 4-2 in round two.
He made it a hat-trick of victories on Saturday by overcoming 64th-ranked Andy Hicks, who made a break of exactly 100, by the same score in round three to book his place in the last 16 on Sunday morning.
Robertson edged out 70th-ranked Li Yan, who compiled a top run of 127, 4-3 in a match where he won all the odd numbered frames and then got the better of 45th-ranked Jamie Jones 4-2 in the quarter-finals.
The 25-year-old former World Amateur Champion eventually succumbed 4-0 at the hands of Matthew Stevens, the world no.15 from Wales who won The Masters in 2000 and UK Championship three years later, in the last four.
St Leonards-based Mark Davis, the world no.17, beat qualifiers Matthew Day (4-1) and Allan Taylor (4-0) in the first two rounds before being pipped 4-3 by Jones in round three.