Gary Wilson became the fifth lowest-ranked player in history to reach the World Championship semi-finals with a 13-9 win over Ali Carter at the Crucible Theatre.
The qualifier, the world number 32 from Tyneside, returned with a 9-7 advantage, building on it immediately with a break of 117 in the opening frame.
Two-time finalist Carter sliced his lead to a solitary frame by taking the next two, helped by a knock of 128, but Wilson flipped the momentum and won three frames on the spin to progress.
Wilson will face Judd Trump in the last four after the Masters champion rounded off a 13-6 win over Stephen Maguire. Trump held an 11-5 lead after their second session on Wednesday afternoon, and finished off breaks of 68 and 82 after Maguire rolled in a 122 to close to 11-6 behind.
Leading 7-1 overnight it looked as if Trump might wrap things up quickly when he won the first two frames of the session to move 9-1 clear.
However, Maguire dug deep and won four of the following five frames, including a break of 110 to force a final session.
Gilbert is through to the semi-finals for the first time in his career as he saw off Kyren Wilson 13-8.
Gilbert led 10-6 from the previous night's session but Wilson battled back a bit by winning two of the first three frames to move to within three of his opponent, but the 16th seed steadied himself as knocks of 56, 60 and 63 carried him into the last four.
Gilbert is the man who recorded the 147th professional 147 and is now guaranteed the biggest payday of his career of at least £100,000.