The Ospreys-bound centre played in a youthful Wales team in the 23-10 victory over the Pumas that included the likes of Adam Beard, Aaron Wainwright and Cardiff Blues duo Seb Davies and Dillon Lewis.
Scarlets playmaker Rhys Patchell kicked ten points while clubmate James Davies grabbed a try, as did wing George North, who joins Ospreys for the upcoming Guinness PRO14 season.
Experienced Welsh players Leigh Halfpenny, Jonathan Davies, Justin Tipuric and Alun Wyn Jones have been rested for the summer tour, with Williams pleased with the options Wales are developing in the build-up to the 2019 Rugby World Cup in Japan.
“A lot of young players have come through and played more rugby now,” said Williams.
Llongyfarchiadau i Gymru ar sicrhau ail fuddugoliaeth ar y daith. Deg pwynt o droed @rhys_patch a chais gan @cubbyboi.
Congratulations to @WelshRugbyUnion. Final score in San Juan Argentina 10 Wales 32. pic.twitter.com/eY7Fqiauv9
— Scarlets Rugby (@scarlets_rugby) June 9, 2018
“James Davies got man of the match, Aaron Wainwright came on and I thought he did really well for his first cap with a couple of turnovers.
“It’s exciting to see young boys like that come on, make an impact, and take their opportunity. I think that’s a credit to the coaches for mixing it up a bit and giving some opportunities to put the jersey on to other people.
“We had quite a lot of young boys out there, but I thought we showed quite a bit of maturity. It’s great to have competition for places, it keeps you on your toes, and it ups your game.
“The strength in depth we’re creating is very exciting and if you think about everyone who has been left out of this tour and the amount of people back at home, it can only be a good thing.”
Wales now head to Sante Fe for the second Test against Argentina, where they’ll play at the 47,000-seater Brigadier General Estanislao Lopez Stadium with the chance to claim a first series win in the country since 1999.
“We’ve gone quietly about our business on this tour and we’ve been quietly confident,” added the 27-year-old centre.
“But there is still another test to go and I’m sure Argentina will look back at this game and be very disappointed to lose at home and in front of their crowd. We’re expecting them to come out hard.
“We want to end this tour with three wins from three.”