Jose Mourinho picked a relatively youthful side, and paired Rashford up front with Jesse Lingard.
Rashford has flitted in and out of the first team, but has predominantly been played in a wider berth.
Manchester United player ratings against Chelsea Sun, April 16, 2017
Express Sport rates how the Manchester United players performed during their win over Chelsea at Old Trafford
Play slideshow REUTERS 1 of 15
Which Manchester United players impressed during their win over Chelsea?
Marcus Rashford scored the opener against Chelsea
Jose Mourinho's tactical gamble paid off
Jose Mourinho crouching during the win over Chelsea
Rashford has made it difficult for him to leave him out. I think he's a very exciting young talent
After a relatively lean spell, Rashford scored his second goal in as many weeks as a resurgent United put themselves back in the frame to finish in the top four.
And Souness thinks Rashford has given Mourinho a selection dilemma for the remainder of the season.
Get Quotes on Home Insurance
“Before the game he said it was because they were tired and then after the game he said he picked the best team,” Souness told Sky Sports.
“I think he has learned something today. Rashford has made it difficult for him to leave him out. I think he's a very exciting young talent.
"He gives them legs and I think he could play with Ibrahimovic. I think it would suit both of them, but that's for the manager to decide.
"United will be very pleased with themselves today and they should be. They've needed to take a scalp here to get the supporters believing again.
"The supporters will be going home tonight believing they've turned a big corner."
United are now fifth in the table, four points behind fourth-placed Manchester City.