The seven-time world champion, making his tournament debut at the Crucible Theatre, had to come from behind on three occasions before winning three successive frames to close out victory.
O’Sullivan had already beaten Ken Doherty (4-1) and Peter Lines (4-2) on Friday to reach the last four, where Milkins provided a tough test during a topsy-turvy contest.
- Sky Sports on WhatsApp: Breaking news, videos and analysis
- Not got Sky? Get Sky Sports or stream contract-free on NOW
- Choose the Sky Sports push notifications you want
Milkins – the former Welsh Open winner – built leads of 3-2, 4-3 and 5-4 to threaten a famous upset against O’Sullivan, who responded with a brilliant 75 break during the 10th frame to level the contest.
O’Sullivan then won the next two frames to complete his victory against ‘The Milkman’, booking a meeting against either Joe Perry or Craig Steadman in Sunday’s best-of-19 final.
“Conditions were really tough,” O’Sullivan said. “None of the players are making excuses.
“I thought we were cueing well, but it is just sometimes you can fall out of position and keep chasing the balls.
“It is hard, especially under pressure in front of a big crowd. So I think we’ve done really well considering the conditions.
“I’m messing about with different types of cue actions so it was a good experience to play under pressure, lose it and get it back. It is all new for me, so I’m enjoying that process.”
Milkins, who defeated Jimmy White in a black-ball decider in the last 16 before beating Igor Figueiredo 4-1 in the quarter-finals, said: “I’m not quite sharp, my match sharpness. I’ve disrespected the game for too long. I was struggling to get back into it. There are signs of playing well, but I just missed too many easy balls.
“Ronnie scares the hell out of me always. I respect Ron. No other player does that to me. It is bad enough playing him when you are playing well. But when you are struggling, you’ve got no chance.”
