The 4yr-old was a winner at Forbury Park on July 17 before heading to Canterbury late last month for two assignments.
The first race - at Rangiora on July 27 - produced a second placing behind subsequent Kurow Cup winner Whozideawasthis.
Four days later, Onedin Mach put on a solid effort to finish third behind the progressive pacer Dalton Bromac and Wesley Silcox.
''He's been beaten by three nice horses in his last two starts,'' Williamson said.
''Back then, he was still very much on the way up. I wouldn't say he's grown a leg since then, but he's improved a great deal since the Canterbury trip.''
Onedin Mach has ended up with a handy draw of barrier 3 for Williamson's junior driver and employee Rory McIlwrick.
''He's got good gate speed so I'll be telling Rory to make use of his draw,'' he said.
''If he found the lead, I'd say he'll try for an all-the-way win and we'll see what happens - he'll either be good enough or he won't,'' Williamson said.
The 4yr-old rounded off his preparation for tonight's 2200m mobile pace with a three-length workout win over Caesars Gamble at Ascot Park on Saturday.
''He got home in about 56.6 [seconds] so I was pleased with that. Put it this way, he's as good as I could have him for this race.''
Williamson entered stablemate Leo in the c2-c3 event so the race would go ahead, despite the 4yr-old being only a c1 pacer.
''It will be a good test for him to see where we are with him. I expect him to give a good account, because he's on the improve.''
Williamson said Leo was for sale, as was Fantasy Dream Girl (race 5), who will be driven by Mitchell Kerr. The Badlands Hanover mare almost rewarded punters when she ran second at Gore on Sunday.
''She's just got a wee bit of a habit in front of switching off. The other one got past her and then she came again.
''Hopefully, if [Kerr] likes her when he drives her, he can buy her.''
Williamson takes the drive behind Mum Beat Lyall in the c1-c2 mobile trot and hopes his magic hands can do the trick.
He has driven the 70-start mare only four times, and only once at Forbury Park, in November 2011, which produced a win.
''She's a talented horse, but she just loves to gallop. If she can forget about that, she'll be there or thereabouts.''
The five-win mare is now back in the c2 grade after last winning in December 2012, and Williamson expects the drop in grade will help.
The best of Williamson's three other drives could be the Andrew Armour-trained Franco Santiago (race 8).
''We'll just see if he makes a clean enough beginning from the stand - Archie's got a bit of an opinion of him, and he usually has them ready.''
