Needing 293 to win, the Lions were in trouble at 235-7 before Malusi Siboto (33*) and Lutho Sipamla (29*) got them over the line.
Kagiso Rapulana top-scored with 88 before being trapped lbw by Dolphins spinner Prenelan Subrayen (2-55).
The Dolphins came into their final fixture having won four games in a row, and the bonus points they picked up in Potch proved to be enough to clinch the title.
It isn't everyday that you see a team celebrating after just losing a match
Then again, it isn't everyday that you know you are officially the champions
Congratulations to the Dolphins for clinching the 4-day series trophy 🔥🏆
📽️ @PVMatch @PitchVision#4DaySeries pic.twitter.com/Hjajy5Q6yR
— Werner (@Werries_) March 15, 2023
Earlier in the day, the second-placed Northerns Titans thrashed the North West Dragons by nine wickets in Centurion, with Neil Brand scoring an unbeaten 95 and Jiveshan Pillay 46*.
At Newlands, spinner Tsepo Ndwandwa took 6-51 as the EP Warriors bowled Western Province out for 259 to claim a 79-run win. Captain Kyle Verreynne top-scored for the hosts with 86.
On Tuesday, the Free State Knights, who had already been relegated to Division 2, completed a nine-wicket win against the Boland Rocks in Paarl.
