Petrie had braced himself for pacesetters Aberdeenshire to seal the glory by beating Grange after his own side had been demolished quickly by Watsonians. But the north-east side imploded in spectacular fashion at Raeburn Place, which means the whole shooting match will be decided in the Granite City on Saturday.
"It was a very bizarre Saturday," admitted Petrie. "Our performance is extremely hard to explain. We usually back ourselves to post a winnable total, even on a tricky track - and that is why I opted to bat after winning the toss.
"I certainly wouldn't blame our defeat on the fact we took first knock - I would credit Sonians for the quality of their new-ball bowling and there is no doubt they thoroughly deserved their win.
For Petrie and co to keep the title they must stave off the challenge of Stoneywood-Dyce at Peoples Park, while also banking on Falkland to pull off a shock win over Aberdeenshire at Mannofield.
n Scotland's match with New Zealand A at Ayr was abandoned yesterday without a ball being bowled.
The Scots had been out for revenge in the second fixture of the thee-game series following Friday's 199-run defeat.
However, the start was delayed after heavy overnight rain left the outfield saturated and, despite the efforts of the ground-staff, further showers meant no play was possible.
The match will now take place on Wednesday at The Grange, Edinburgh, with the final fixture at the same venue 24 hours later.
The Murgitroyd T20 national finals day also fell victim to the weather for the second week in a row.