Wales arrived in Nice from Bordeaux on Monday afternoon and have been preparing for this fixture from their match city training base.
Tomos Williams starts at scrum-half to win his 50th cap for Wales. Gareth Anscombe makes his first appearance of the 2023 world cup campaign at fly-half.
Dewi Lake, one of four players in the starting line-up making their Rugby World Cup debut this weekend, captains the side at hooker. He is joined in the front row by Nicky Smith at loosehead prop and Dillon Lewis at tighthead prop.
Johnny Williams and Mason Grady make their World Cup debuts in the Wales midfield.
In the back three, Leigh Halfpenny is named at fullback to win his 101st cap and features in his tenth RWC match across three tournaments. Rio Dyer makes his first start of the 2023 edition, joining Louis Rees-Zammit on the wing.
Club teammates Christ Tshiunza and Dafydd Jenkins pair up in the second row with Tshiunza making his first start at lock for Wales.
The back row is made up of Dan Lydiate at blindside flanker who, like Halfpenny, is making his tenth RWC appearance in his third tournament, Tommy Reffell making his first start of this year’s tournament at openside flanker and Taulupe Faletau at No. 8.
Wales’ replacements include Gareth Davies, Sam Costelow and Josh Adams as the back line cover.
Ryan Elias, Corey Domachowski and Tomas Francis are the front row cover, Adam Beard is the second row cover and Taine Basham, in line for his World Cup debut, is the final forward replacement.
Gatland said: “We’ve made a few changes this week given the six-day turnaround.
“This is an opportunity now for this match day 23. I’ve said before, but there’s some great competition within the squad which is what we want to see. There’s a chance now for this group to go out Saturday and to put down their own marker in the tournament.
“We’ve done a thorough debrief of last week’s game and know the areas we need to improve. We have a clear plan of how we want to play on Saturday and it’s about going out there and executing that as we have prepared.
“Portugal are a skillful side and will be raring to go this weekend in their first match of the tournament. We’re excited to get back out there and looking forward to seeing more great support from the travelling fans out in Nice.”
Wales senior men’s XV to play Portugal at Stade de Nice. Pool C, Rugby World Cup 2023
Saturday 16 September, KO 4.45pm BST. Live on ITV and S4C.
15. Leigh Halfpenny (unattached – 100 caps)
14. Louis Rees Zammit (Gloucester Rugby – 28 caps)
13. Mason Grady Cardiff Rugby – 4 caps)*
12. Johnny Williams (Scarlets – 6 caps)*
11. Rio Dyer (Dragons – 10 caps)
10. Gareth Anscombe (Suntory Sungoliath – 35 caps)
9. Tomos Williams (Cardiff Rugby – 49 caps)
1. Nicky Smith (Ospreys – 44 caps)
2. Dewi Lake (Ospreys – 9 caps)*
3. Dillon Lewis (Harlequins – 52 caps)
4. Christ Tshiunza (Exeter Chiefs – 7 caps)*
5. Dafydd Jenkins (Exeter Chiefs – 8 caps)
6. Dan Lydiate (Dragons – 71 caps)
7. Tommy Reffell (Leicester Tigers – 11 caps)
8. Taulupe Faletau (Cardiff Rugby Caerdydd – 101 caps)
16. Ryan Elias (Scarlets – 35 caps)
17. Corey Domachowski ( Cardiff Rugby – 3 caps)
18. Tomas Francis (Provence Rugby – 73 caps)
19. Adam Beard (Ospreys – 48 caps)
20. Taine Basham (Dragons – 13 caps)*
21. Gareth Davies (Scarlets – 70 caps)
22. Sam Costelow (Scarlets – 5 caps)
23. Josh Adams (Cardiff Rugby – 51 caps)
*player making RWC debut