Du Plessis finished with an unbeaten 38 off 27 balls as the 27-year-old continues to live up to his tag as one of the best finishers in South Africa, taking the Titans to their target of 157 with nine balls to spare.
Farhaan Behardien was with him at the end on 12 not out, scoring the winning runs with a tremendous six over extra cover off left-arm paceman Beuran Hendricks.
The target could have been a tricky one on a two-paced pitch against a Cobras attack that only had one quickish bowler and four spinners, but Henry Davids (24 off 17), Roelof van der Merwe (18 off 13) and Martin van Jaarsveld (24 off 18) provided the attacking impetus that gave the likes of Heino Kuhn (25 off 26), Du Plessis and Berhardien the freedom to play sensibly without taking risks.
The openers – Davids and Kuhn – gave the innings the ideal start as they added 48 in six overs. Davids showed great hands as he drove the ball inside-out superbly, collecting two sixes and a four in his 24.
Davids fell when he charged down the pitch and missed a slash at legspinner Alistair Gray, and Kuhn departed two overs later when he top-edged a reverse-sweep at offspinner Dane Piedt and was caught at short third man.
Justin Kemp and Dane Vilas combined superbly to dismiss Van der Merwe, although there was some doubt as to whether the batsman actually gloved a surprise bouncer that was brilliantly taken by the wicketkeeper standing up to the stumps.
There might have been some concern in the Titans camp with the score 74 for three at the halfway mark, but captain Van Jaarsveld threw the bat at anything remotely wide as he collected four fours off 18 balls.
Van Jaarsveld was stumped by Vilas off Gray in the 15th over, but with just 35 runs still needed, the Cobras knew their hopes of staying in contention for the playoffs were almost gone.
Du Plessis and Behardien calmly finished the match at the behest of their appreciative home crowd, but the Titans’ failure to secure the bonus point means their hopes of finishing top of the log and hosting the final are gone.
Even if the Titans get a bonus-point win over the Warriors on Wednesday, they can only draw level with the Lions’ current total of 35 points.
The applicable tie-breaker then is the results of matches between the Lions and the Titans, with both teams having seven outright wins overall. Unfortunately for Matthew Maynard’s team, the Lions won both of their round-robin contests.
Wrist-spinner Brad Hogg was the best of the Cobras bowlers, conceding just 16 runs in his four overs, but the visitors obviously lacked quality back-up and four spinners was perhaps overkill.
The Nashua Mobile Cape Cobras had earlier made run-scoring look difficult as they cobbled together 156 for six, although there were certainly hints of inconsistent bounce and spinners Eden Links and Van der Merwe both obtained noticeable turn.
Richard Levi more often than not makes run-scoring look easy when he charges at the top of the innings, and he bashed a quickfire 25 off 13 balls to give the Cobras a good start after they had won the toss and elected to bat.
The Cobras were 30 without loss after three overs thanks to Levi, but the Titans fought back as they claimed three wickets and conceded just 37 more runs in the next seven overs.
Albie Morkel removed Levi with his first ball, Behardien hanging on to a rocket of a catch at cover, and Yaseen Vallie (6) and Owais Shah (12) both fell cheaply as they misjudged slower balls from Alfonso Thomas and Morkel respectively.
Stiaan van Zyl and Vilas steadied the innings as they added 26 off 27 balls for the fourth wicket, before Van Zyl was bowled by Van der Merwe for 33, backing away and trying to deliver a big hit.
The Titans were in control as Morkel stood at the top of his mark at the Hennops River End with the Cobras on 120 for five after 18 overs.
But having bowled so well previously, taking two for 10 in three overs, Morkel’s final over was the one that allowed the visitors to substantially up their run-rate, Vilas and Kemp taking 27 runs from it.
The first ball of the over was up to the bat and driven majestically over cow-corner for six by Vilas, and even the Titans crowd clapped when Kemp pulled the last two balls of the over for sixes in the same vicinity.
It meant Morkel finished the innings with tired old figures of two for 37 in four overs, but the Cobras were still up against it at the other end, where Thomas closed with two overs for 13 runs and picked up the wicket of Kemp, who hit a slower-ball full toss off the toe of the bat, slapping a return catch.
Kemp’s 24 off 18 balls was a crucial contribution, but the real hero of the Cobras innings was Vilas, whose 48 not out off 28 balls was a top-class innings.
His composure and a talent for hitting boundaries in the closing overs provided a mighty boost to the innings as he collected four fours and two sixes.
The Titans bowling was a mixed bag. Ethy Mbhalati, Morkel and Van der Merwe were all expensive, while Links, David Wiese and Du Plessis bowled seven overs for 46 runs between them. Thomas’s figures of two for 22 in four overs took the cake, however.