Gloucester's Milkins made the 147 in the third frame, on his way to taking a 6-3 lead. He needs four more frames tonight to complete victory.
Milkins was already the only player to have made a 147 in the qualifying rounds of the World Championship, having done so in 2006 in a match against Mark Selby.
Today's effort was worth £1,500 for the rolling 147 prize, as well as £1,000 for the pre-TV high break prize, as long as another player does not make a 147.
The maximum from Milkins was the tenth of the season and 87th in snooker history.
Ball by ball scoring and results from tournaments