There are four Ospreys in the starting side, with Lee Byrne, Tommy Bowe and Mike Phillips included in the backline and Alun-Wyn Jones named at lock. Prop Adam Jones wins a place on the bench to take the total number to five.
Magners League Champions Munster have four squad members, with captain Paul O'Connell and openside flanker David Wallace in the first XV and Donncha O'Callaghan and Ronan O'Gara among the replacements.
Cardiff Blues and Leinster contribute two players each to the starting line up and another to the matchday 22.
Jamie Heaslip and Brian O'Driscoll are the Leinster starters, while Rob Kearney has recovered from a dead leg he suffered in Saturday's win over Western Province to take a place on the bench.
Starters Jamie Roberts and Gethin Jenkins and replacement Martyn Williams are the Blues contingent, while fellow Welsh region the Scarlets have Stephen Jones starting at outside-half and Matthew Rees providing cover for Lee Mears at hooker.
"The Test team has been picked on form following the six provincial matches," said McGeechan, who has overseen six successive provincial victories so far on the 10-match tour.
"There were some very difficult calls to make as the players as a group and individually have done everything that we have asked of them and performed on the field.
"The preparation for the First Test has been very positive. It has been a challenge to reach the First Test with an unbeaten record as we have played a variety of provincial teams across the country.
"This challenge is a unique one in the modern rugby calendar in that it comes only in a Lions context these days. The players have had to adapt to preparing and playing more frequently. They have answered that challenge.
"It has been 20 years since a Lions team has won all of its' provincial matches leading up to the Test series so it is very satisfying to be in such a position. The entire squad and the management have worked hard to create an outstanding team environment. Everyone has done this very professionally and it is fair to say that I would not change anything that we have done so far."
"Playing South Africa on its home soil is one of the ultimate challenges for the British & Irish Lions," added Davies, who was a victorious Lion in New Zealand 38 years ago.
"South Africa also happen to be world champions which adds an extra edge to the series, just as it did in 1997.
"The tradition between the Lions and the Springboks is legendary and after the six lead up provincial matches the rugby world is waiting with great anticipation for the First Test in Durban this Saturday."
Lions (vs South Africa, first Test, Saturday June 20)
15. Lee Byrne (Ospreys/Wales)
14. Tommy Bowe (Ospreys/Ireland)
13. Brian O'Driscoll (Leinster/Ireland)
12. Jamie Roberts (Cardiff Blues/Wales)
11. Ugo Monye (Harlequins/England)
10. Stephen Jones (Scarlets/Wales)
9. Mike Phillips (Ospreys/Wales)
8. Jamie Heaslip (Leinster/Ireland)
7. David Wallace (Munster/Ireland)
6. Tom Croft (Leicester Tigers/England)
5. Paul O'Connell (Munster/Ireland) Captain
4. Alun-Wyn Jones (Ospreys/Wales)
3. Phil Vickery (London Wasps/England)
2. Lee Mears (Bath/England)
1. Gethin Jenkins (Cardiff Blues/Wales)
Replacements
16. Matthew Rees (Scarlets/Wales)
17. Adam Jones (Ospreys/Wales)
18. Donncha O'Callaghan (Munster/Ireland)
19. Martyn Williams (Cardiff Blues/Wales)
20. Harry Ellis (Leicester Tigers/England)
21. Ronan O'Gara (Munster/Ireland)
22. Rob Kearney (Leinster/Ireland)
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