At 1-85 through 12 overs with marquee Jameel Qureshi and stand-in skipper Andrew Brown set and comfortable at the crease, the Saints looked likely to cruise past CYMS' 5-143.

Qureshi's dismissal for 42 three overs later, with the score at 100, changed the game.

He'd been doing it easy since joining Brown (43 not out) at 1-41 earlier in the dig but when he was lured into a false shot by Luke D'Elboux (1-8) momentum swung, and CYMS tightened the screws.

They only snared one more wicket but held the reigning champions to 3-133 and take a massive, tournament-opening scalp.

"[Qureshi] was manipulating the field with ease out there. The class players do that so we were looking for dot ball pressure, trying to get him to get hit to areas he didn't want to and we got the wicket, that changed the chase," CYMS skipper Hugh Le Lievre said.

"They finished 11 short but only three down so I think we've done a great job to peg them back ... but, to be honest, I didn't really feel like we were in control of that game until the last five overs or so.

"Still, they're the team to beat and to be do that in the first round, all speed to us in the Twenty20 competition."

Switching things up and bowling spin, Mick Delaney (1-14) and Chris Novak (0-29) both proved tough to get away as did D'Elboux, while Le Lievre (0-25) conceded just eight in the final over - the Saints required 19.

Delaney and Novak bowling spin rather than seam-up wasn't based on Sunday's conditions, although Le Lievre said it did play into CYMS' hands.

"I think they'll both be bowling spin full-time but it worked well. I think St Pat's maybe left it a bit too late to bowl their slower bowlers on that wicket and we learned from it, Pup (Delaney) and Novsy both bowled really well," he said, before lauding the entire side's effort.

"It was a good quality, team effort and I think that's the way to win Twenty20 games. With the bat my brother Angus (66), Dave Neil (31 not out) and Pup (19) all played well, they laid a good, solid platform."

St Pat's are now expected to have to win all three of their remaining preliminary games against Kinross, Cavaliers and Bathurst City if they're to win a spot in the final four.

"It's not ideal, no, but we did it at Centennials last year, dropping the first one then making the semi-finals so it's not out of the question," Brown, who has linked with the Saints from the Bulls this summer, said.

"We let that game get away from us, definitely. We were going along well but once Jameel got out I just couldn't get it away and [the required run rate] just crept up.

"CYMS bowled well at the end though, you have to give them credit."

CYMS' win was the first game of Sunday's double-header at Wade Park. Bathurst City were taking on Kinross in the afternoon, with that game still in process at time of publication.