The 27-year-old Potteries professional reached the quarter-finals of the pounds 325,000 event with a 5-2 victory that included two century breaks.
Now he faces McManus's fellow Scot Stephen Hendry, looking to gain revenge for a 13-2 drubbing in last season's world championship. He had waited four years to avenge a defeat by his Scottish rival in the pro-ticket qualifiers that delayed his entry into the professional ranks by 12 months.
'I scored really heavily and my safety play matched Alan's,' said Harold, whose 140 in frame two equalled the highest ever during the televised stages. He almost compiled another 140 two frames later but finished on 113 for a 3-1 interval lead.
Harold was a 500-1 outsider when he won last season's Asian Open, beating Hendry along the way. This time his odds are 20-1 as he moves to within three games of the pounds 60,000 top prize.
Manchester's Joe Swail, the world No 12, defeated one of the tournament's surprise packets, Wayne Brown, 5-3 to earn a quarter-final place against Jimmy Michie, of Pontefract. 'I'm disappointed because I've played much better in my other matches,' Brown said.Reuse content