Earlier, James Vince's unbeaten half century had sent Multan Sultans into the playoffs after a thumping nine-wicket victory over Islamabad United in yet another rain-shortened game at Rawalpindi.
The 32-year-old Dunk cashed in on an early dropped catch to bludgeon an unbeaten 99 off 40 balls that also featured three fours as Lahore reached 190-2 with five balls to spare.
Karachi's Alex Hales also profited from an early let-off to score 80 not out and Chadwick Walton made 45 off 20 balls in what had appeared to be a competitive 187-5 after hosts Lahore won the toss and opted to field.
Dunk had smashed 10 sixes in Lahore's victory over Quetta Gladiators in this edition before raising his own PSL record by hitting two more to earn Lahore its third win in the tournament. He brought about the win with his 12th six by hoisting Cameron Delport over the long-off boundary.
Dunk was ably supported by captain Sohail Akhtar, who scored 68 not out off 46 balls, but the skipper took the back seat in an unbeaten 140-run partnership off 65 deliveries with the Australian.
Dunk had provided an opportunity when he was on 11, but substitute fielder Mohammad Rizwan missed a regulation catch at deep midwicket. Dunk went on to punish the two leftarm spinners — captain Imad Wasim (0-40) and Umer Khan (1-37). Imad also dropped a hard catch off his own bowling but by then Dunk had reached 69 and taken the game away from Karachi.
The resounding victory lifted Lahore from the bottom of the table with six points and it is still in with a chance to qualify for the playoffs with three games in hand. Defending champion Quetta also has six points but is last on net run-rate. Karachi is fourth with seven points from seven games.
At Rawalpindi, Vince plundered 11 fours and a six in his 61 not out off only 24 balls as Multan motored to 94-1 in 6.4 overs against two-time champion Islamabad.
After a wet outfield due to overnight rain curtailed the match to nine overs a side at the Pindi Cricket Stadium, Islamabad could only score 91-7 despite Colin Munro (25 off 12) hitting veteran Shahid Afridi for three successive sixes in the fourth over.
Multan's other legspinner Imran Tahir (2-13) and left-arm fast bowler Junaid Khan (2-17), playing his first game in this PSL season, then shut down Islamabad in the latter half of the innings.
Imran got rid of the dangerous Munro off his third ball when the left-hander top-edged a slog sweep to short fine leg. Captain Shadab Khan (14) also holed out in the deep against Imran's legspin.
Junaid, who had earlier got rid of opener Luke Ronchi, then had Asif Ali caught off his own bowling as Islamabad could score only 39 runs in the last five overs.
Vince took the game away when he slammed five successive boundaries against seamer Akif Javed in only the second over of Multan's run chase. Legspinner Shadab was plundered for 30 runs off his two overs as Multan chased down the target with 14 balls and nine wickets to spare.
Multan is top with 11 points from seven games in the six-team event. The top four qualify for the playoffs.
After losing its fourth home game on Sunday, Islamabad is in a tight corner with seven points from nine games. It faces Karachi next Saturday.