Hetmyer's spell at the crease, laced with three sixes, brought Rajasthan past Punjab's 147-8 with only one ball to spare, cementing the side's place at the top of the table with only one loss from the season so far.
"Sometimes it happens, sometimes it doesn't," Hetmyer said. "Happy I could help my team win tonight."
Punjab got off to a decent start with Atharva Taide and Jonny Bairstow making 26 runs for no loss at the end of three overs. But Avesh Khan dismissed Taide soon after while Bairstow fell in the eighth over - both making 15.
Rajasthan's clinical bowling choked the innings, with Keshav Maharaj sending back acting captain Sam Curran for six. Impact sub Ashutosh Sharma top-scored from the bottom order with 31 from 16 balls before he was caught on the last ball of the innings off Trent Boult.
Rajasthan openers Yashasvi Jaiswal and Tanush Kotian set up the chase with a 56-run partnership before Liam Livingstone bowled the latter for 24 in the ninth over.
Fast bowler Kagiso Rabada removed Jaiswal (39) and Sanju Samson (18), with Hetmyer coming in at the end of the 17th over when the visitors were still 35 behind. He slammed two boundaries in the 18th over and powered through even as partners Rovman Powell (11) and Maharaj (one) fell.
"A little disappointed and we will bounce back in the next game," Curran said.
