Centre-back Watts joined League One side Wigan Athletic on Monday, just prior to their trip to Hull City in the second round.
And the 21-year-old started for the Latics and was on the pitch as goals from Wigan's Stephen Humphrys and Hull's Keane Lewis-Potter levelled the score at 1-1.
Watts was then replaced with 15 minutes remaining as James Carragher, son of former Liverpool hero Jamie, came on for his debut.
And Leam Richardson's men prevailed in the ensuing penalty shoot-out, winning 8-7 to book their place in the second round.
Cass, meanwhile, was named on the bench for Port Vale's League Two opener at Northampton Town on Saturday.
But the full-back, who spent last term on loan at Hartlepool United, did make his debut for the Valiants in their cup clash with Sunderland on Tuesday.
The 21-year-old came off the bench with 25 minutes remaining and, though Jamie Proctor pulled a goal back for his side just two minutes later, he couldn't prevent his new club from falling to a 2-1 defeat.
Photograph courtesy of Dean Edwards/Wigan Athletic