The 31-year-old Duckett made 64 from 47 balls, including five consecutive fours off Liam Patterson-White to bring up his fifty from 35 deliveries, as the hosts posted 146 for four at Trent Bridge.
Duckett was supported by Aneurin Donald, who marked his Rockets debut by smashing three sixes in a 19-ball 40. Aussie Tim David weighed in with an unbeaten 24.
A 71-run third-wicket stand between Marsh and Harry Brook had put SunRisers in control of their chase, with just 35 runs required from 20 deliveries.
However, Mohammad Amir conceded only five runs off the next four balls before Brook was brilliantly caught by diving England team-mate Duckett for 46.
Amir had Marsh caught by Sam Billings for 41 five balls later to finish with 2-20 as Rockets held on to claim a fourth straight win and extend their lead at the top.
In the day's other match Rashid Khan's five-wicket haul inspired MI London to a dominant 45-run win over Manchester Super Giants.
The Afghanistan spinner returned figures of 5-17 after half-centuries from Will Jacks and Nicholas Pooran powered the hosts to 6-183 at the Oval.
MI London opener Jacks smashed six sixes in a blistering 62 from 31 deliveries before Pooran added four more in a 28-ball 54.
Super Giants spinner Noor Ahmad dismissed Jacks, caught by Aiden Markram, and later had Sam Curran stumped by Jos Buttler for 23, while Josh Tongue took 2-13, including the wicket of Pooran.
Markram led the reply with a rapid start during the powerplay before Rashid removed Tim Seifert for 17 and Buttler for two.
South African opener Markram reached 50 from just 25 deliveries but fell off the very next ball he faced, caught by Curran off spinner Nathan Sowter.
Star man Rashid then dismissed Heinrich Klaasen for 13, Tom Moores for a duck and Liam Dawson for two in quick succession to complete his five-for.
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