But after the break, Canterbury looked a completely different side – bursting out of the tunnel to almost cross over within minutes, settling for three points instead.
Helped by a superb performance from newly selected All Black George Bridge, Canterbury turned the screw and pinned Tasman in their own 22 for the majority of the second half.
And the pressure kept coming for Tasman – slowly losing the scrum battle, second to loose balls – who simply struggled to keep with the pace and power of the Cantabrians.
Eventually they were broken down, with Canterbury captain Mitchell Drummond crossing over off a scrum. A nicely struck kick from the sideline by Brett Cameron tied it at 16-all after 63 minutes.
From there, there was only going to be one result especially after Will Jordan was sent to the bin for a deliberate knockdown, Tasman's second yellow card of the half.
It was the skipper again in the end who jumped on a nicely weighted grubber to break Tasman's hearts and set up a chance to claim their fourth straight Mitre 10 Cup title.
Canterbury will face the winner of tomorrow's other semifinal between Auckland and Wellington.
Canterbury 21 (Mitchell Drummond 2 tries; Brett Cameron 3 pen, con)
Tasman 16 (David Havili try; Mitch Hunt 3 pen, con)
Halftime: 6-13.