Delhi down Rajasthan to stay in the race for IPL playoffs
Delhi posted 221-8 courtesy of Jake Fraser-McGurk's 20-ball 50 and an attacking 65 by Abishek Porel at their home Feroz Shah Kotla ground.
Rajasthan looked good in their chase after Samson's fifth half-century of this season but his dismissal, a catch in the deep which was ruled clean by the third umpire, turned the match in Delhi's favour.
Rajasthan, who are yet to confirm their play-off spot, lost three more wickets in the next two overs and Delhi restricted the opposition to 201-8 for their sixth win in 12 matches.
"We had it in our hands, it was 10-11 runs per over which was achievable but these things happen in the IPL," Samson said after the loss.
Inaugural champions Rajasthan, placed second behind toppers Kolkata Knight Riders, have eight wins in 11 matches and still favourites to make the top two in the play-offs.
Top four teams will make the play-offs but number one and two will have the advantage of getting an extra match to enter the final on May 26 in Chennai.
Spinner Kuldeep Yadav returned impressive figures of 2-25. Fast bowlers Khaleel Ahmed and Mukesh Kumar also took two wickets. But the batters set up victory after Fraser-McGurk, who raised his 50 in 19 balls, and Porel attacked in an opening stand of 60.
Rajasthan lost wickets after the openers departed but Tristan Stubbs hammered 41 off 20 balls in a late charge to take the total to 221-8.
Stubbs was helped by Gulbadin Naib, who hit 19, and Rasikh Salam, who hit two sixes in his nine runs, as Delhi got 53 runs from the last three overs.
The in-form Samson, a wicketkeeper-batsman who has amassed 459 runs, attempted to set up the chase only to depart in the 16th over when Shai Hope caught the batsman off Kumar.
Hope's foot was parallel to the boundary rope but the third umpire ruled it out and a disappointed Samson walked back after a chat with the on-field officials.
Veteran spinner Ravichandran Ashwin led the Rajasthan bowling with figures of 3-24.
Yuzvendra Chahal took his 350th T20 wicket - the first Indian to achieve the feat - when he got skipper Rishabh Pant, a left-hand batsman, caught out at fine leg for 15.