The match required two Super Overs after both sides finished regulation tied on 134.
The hosts had battled to 134-8 after choosing to bat, their innings held together by a vital 42-run stand between Keith Dudgeon (28*) and Fersico Adams (24).
Earlier, Grant Roelofsen (18) and Lehan Botha (21) added 32 for the third wicket, but regular strikes - including Jon-Jon Smuts's tidy 4-0-20-2 - kept Boland in check.
The Dolphins' chase stuttered to 84-7, with Dudgeon (3-27), Glenton Stuurman (2-30) and Imraan Manack (1-17) dismantling the top order.
Only Gomolelo Phiri stood firm, hammering 53 from 37 balls with four sixes. Needing one off the final delivery, he was run out attempting a desperate single, sending the contest to a Super Over.
The Dolphins posted seven in the first decider, du Plooy clearing the rope before Stuurman dismissed both Phiri and Bryce Parsons. Boland matched the seven without loss, forcing a second shoot-out.
This time Roelofsen and Clyde Reeves-Fortuin mustered 10, the last ball racing to the fence. Stuurman then struck again as du Plooy fell to Jhedli van Briesies at long-on, and with the Dolphins finishing on 5-1, Boland sealed a remarkable win.
Titans hold off Dragons in Potchefstroom run-fest
At Senwes Park, the Titans survived a spirited chase from the North West Dragons to clinch a seven-run victory in a high-scoring thriller.
After piling up 196/6, the visitors were powered by Heinrich Klaasen's blistering 53 off 31, Andile Phehlukwayo's composed 43, and Dayyaan Galiem's 35, with Donovan Ferreira adding a rapid 22 off 10. Onke Nyaku led the Dragons' attack with 2/33.
The hosts replied strongly, reaching 189/6 thanks to Lesiba Ngoepe's superb 65 from 40 and Wihan Lubbe's fluent 46.
Yet disciplined spells from Lungisani Ngidi (2/38), Galiem and Duan Jansen ensured the Titans stayed just ahead, eking out a tense win in the closing overs.
WSB Western Province kept their CSA T20 Challenge playoff hopes alive with a commanding nine-wicket victory over the Moothee Ram Tuskers at the City Ground in Pietermaritzburg on Thursday.
The North West Dragons beat the KZN Tuskers in Potchefstroom while the Warriors comfortably saw off the Lions in Gqeberha in CSA T20 Challenge fixtures on Tuesday.
The Dolphins defeated the Warriors by seven wickets at Kingsmead Stadium with Western Province completing an emphatic 85 run victory over the Titans on Sunday.
Cameron Shekleton struck a fifty while a late cameo from Wayne Parnell helped the KZN Tuskers seal their first victory of this season's CSA T20 Challenge after a two-run win against the Lions at the Wanderers.
