Selby won the final three frames to edge Allen 6-5, while Gilbert won all three frames after the interval to beat Ford 6-3.
Allen was within touching distance of victory with a break of 62 in the ninth frame at 5-3 up, but missed a double and Selby went on to take the frame after producing a good snooker then holding his nerve to pot pink and black.
Selby backed his opponent taking the shot on and suggested divine intervention may have helped it stay out.
"If he pots the double he basically wins the match, I think it was the right shot it's only the pace that kept it out," Selby said.
"I watched it back on the highlights and I don't know how it's not dropped. Someone was looking down on me for it not to go in."
After splitting the opening two frames, Selby went into a 3-1 lead with breaks of 82 and 93 but Allen pulled level with a match-high break of 96 in the 6th.
Then followed the marathon 67-minute seventh which Allen ultimately won and he also took the next to move himself within a frame of the final.
Huge fluke on green wins frame for Selby and sends semi-final to decider
The 'Jester from Leicester' could not keep a straight face when a fluke enabled him to win the tenth frame and put the match into sudden death.
Both players had chances in the deciding frame but it was Selby who ultimately held his nerve producing a break of 64 to prevail.
"I thought it was a good game from start to finish, we had one scrappy game...but that was because the safety was so good," Selby said.
In the second semi-final, Ford won the first frame but lost the next three before the interval but breaks of 102 and 74 left the match all square.
Then Gilbert recorded a 134 break of his own and two fifties to bring him to the brink of victory, eking out his path to the final where he will meet his practice partner.
"Mark's one of my favourite players, I'm very lucky over the last couple of years he's moved to Nuneaton and he's allowed me to practice with him," Gilbert said.
"He's a reason why I've improved so much."