Williams is named on the wing for his landmark appearance and he will line-up alongside debutant full-back Holmes and Scarlets wing Steff Evans in the back-three.
In the pack Wyn Jones makes his first start for Wales, with all nine of his current appearances coming from the bench. Jones packs down alongside Dragons duo Elliot Dee and Leon Brown in the front-row.
Adam Beard keeps his place in the second-row and is joined by Jake Ball, who has overcome injury to return to the Wales line-up for the first time since last autumn.
— Welsh Rugby Union ? (@WelshRugbyUnion) November 15, 2018
Davies, who has been training with the squad during spells this autumn, is officially called into the squad and will make his seventh appearance for Wales.
“Saturday is a fantastic opportunity for a number of players,” said head coach Warren Gatland. “It’s Jonah’s first game which is exciting and Liam reaches his 50th which is a great achievement.
“We are looking forward to the challenge of Tonga. They had a great win last weekend against the French Barbarians and we know it is going to be a tough, physical challenge.
“We have spoken about creating depth and for us that is all about creating a squad that is full of first-teamers, everyone in the squad capable of starting. The boys this weekend have to put their hand up for the final match and put pressure on the players who started last weekend.
“Ellis captains the team for the second time whilst making his first start at home and for Wyn, it is his first start in about nine appearances off the bench.
“It’s important to realise when selecting a team that we look at all these things in terms of experience, starts, depth balance and opportunity, and all that goes into the mix.”
On the bench Ryan Elias, Rob Evans and Tomas Francis provide the front-row cover with Cory Hill and Ross Moriarty completing the forward contingent. Aled Davies, Rhys Patchell and Josh Adams provide the back-line cover.
WALES TEAM TO PLAY TONGA (Saturday November 17, KO 2.30):
15. Jonah Holmes (*Uncapped)
14. Liam Williams (49 Caps)
13. Tyler Morgan (4 Caps)
12. Owen Watkin (6 Caps)
11. Steff Evans (11 Caps)
10. Dan Biggar (63 Caps)
9. Tomos Williams (4 Caps)
1. Wyn Jones (9 Caps)
2. Elliot Dee (11 Caps)
3. Leon Brown (4 Caps)
4. Jake Ball (28 Caps)
5. Adam Beard (6 Caps)
6. Aaron Wainwright (1 Cap)
7. Ellis Jenkins (9 Caps) (Capt)
8. Seb Davies (6 Caps)
16. Ryan Elias (5 Caps)
17. Rob Evans (29 Caps)
18. Tomas Francis (34 Caps)
19. Cory Hill (20 Caps)
20. Ross Moriarty (25 Caps)
21. Aled Davies (11 Caps)
22. Rhys Patchell (10 Caps)
23. Josh Adams (5 Caps)
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