The defeat sees the Castle Lager Lions Series level at 1-1 going into this weekend’s final Test match.
The Tour’s leading try-scorer, Adams (Wales), makes his Lions Test debut on the right wing joining Duhan van der Merwe (Scotland) who keeps his place on the left. Williams (Wales) is added at fullback to complete the back three.
Bundee Aki (Ireland) is included at inside centre to win his first Test cap, joining Robbie Henshaw (Ireland) who switches to 13.
Dan Biggar (Wales) is retained at flyhalf with Ali Price (Scotland) starting at scrumhalf having been named as a replacement last weekend.
In the pack, there are two changes to the front-row with injury-free Wyn Jones (Wales) taking his place on the loosehead to make his Lions Test debut alongside Ken Owens (Wales), who is promoted from the bench to start his first Test of the Tour at hooker. Tadhg Furlong (Ireland) continues on the tighthead to win his sixth-successive Test cap.
Alun Wyn Jones (Wales) is named as captain to win his 12th consecutive cap moving him alongside Graham Price (1977-1983) and Mike Gibson (1966-1974) in the list of most Lions Test appearances. The iconic Welshman is again partnered in the second row by Maro Itoje (England).
The back row remains the same with Courtney Lawes (England) at blindside flanker, Tom Curry (England) on the openside and Jack Conan (Ireland) at No 8.
On the bench, Adam Beard (Wales), Finn Russell (Scotland), and Sam Simmonds (England) feature for the first time in the Test Series and will all win their first Lions cap should they take the field.
Kyle Sinckler (England) is included subject to the outcome of a disciplinary hearing.
“The matchday 23 have an incredibly special opportunity in front of them – to seal a Lions Series victory in South Africa,” said Gatland.
“It doesn’t get much bigger than this and we’re excited by the challenge that faces us on Saturday.
“We’ve no excuses from last week, the Springboks put us under pressure in the second half and deserved the win. We have to be much better than that second half performance, and I believe we will be.”
British & Irish Lions team for third Test:
15. Liam Williams (Scarlets, Wales) #833
14. Josh Adams (Cardiff Rugby, Wales) #836
13. Robbie Henshaw (Leinster Rugby, Ireland) #824
12. Bundee Aki (Connacht Rugby, Ireland) #837
11. Duhan van der Merwe (Worcester Warriors, Scotland) #841
10. Dan Biggar (Northampton Saints, Wales) #821
9. Ali Price (Glasgow Warriors, Scotland) #843
8. Jack Conan (Leinster Rugby, Ireland) #839
7. Tom Curry (Sale Sharks, England) #853
6. Courtney Lawes (Northampton Saints, England) #826
5. Alun Wyn Jones – captain (Ospreys, Wales) #761
4. Maro Itoje (Saracens, England) #825
3. Tadhg Furlong (Leinster Rugby, Ireland) #818
2. Ken Owens (Scarlets, Wales) #829
1. Wyn Jones (Scarlets, Wales) #842
16. Luke Cowan-Dickie (Exeter Chiefs, England) #851
17. Mako Vunipola (Saracens, England) #787
18. Kyle Sinckler (Bristol Bears, England) #814 – subject to outcome of disciplinary hearing
19. Adam Beard (Ospreys, Wales) #852
20. Sam Simmonds (Exeter Chiefs, England) #849
21. Conor Murray (Munster Rugby, Ireland) #790
22. Finn Russell (Racing 92, Scotland) #835
23. Elliot Daly (Saracens, England) #822