Ritchie, appointed captain just this month, comes onto the flank in place of Rory Darge, who is out with an ankle injury.
There were five alterations to the pack announced on Thursday, from the team that narrowly lost to Argentina in Salta at the end of a closely fought series in July.
Ewan Ashman, Jonny Gray and Rory Sutherland are unavailable on Saturday because they are based at clubs outside of Scotland and the test falls outside the window for internationals.
Townsend had earlier unexpectedly omitted mercurial flyhalf Russell, and stripped Stuart Hogg of the captaincy, although the British & Irish Lions fullback is expected to play in the tests against Fiji, New Zealand and Argentina next month. Neither played toured Argentina in the summer.
With Townsend only able pick Scottish-based players on Saturday, prop Pierre Schoeman replaces Sutherland, Dave Cherry comes in for Ashman at hooker and Grant Gilchrist takes the place of Gray at lock.
Sam Skinner will partner Gilchrist in the second row after Scott Cummings was ruled out when he broke a toe in training this week.
Darcy Graham is picked on the wing ahead of Rufus McLean in the only backline change.
Former Australia international Jack Dempsey is named among the replacements and is set for a first cap against his old country.
The Glasgow Warriors number 8 qualifies for Scotland through his Scottish grandfather. Having previously played 14 matches for Australia, Dempsey has made himself available to play for Scotland under World Rugby’s new birthright transfer rules.
Team: 15-Ollie Smith, 14-Darcy Graham, 13-Mark Bennett, 12-Sione Tuipulotu, 11-Duhan van der Merwe, 10-Blair Kinghorn, 9-Ali Price, 8-Matt Fagerson, 7-Hamish Watson, 6-Jamie Ritchie (captain), 5-Grant Gilchrist, 4-Sam Skinner, 3-Zander Fagerson, 2-Dave Cherry, 1-Pierre Schoeman
Replacements: 16-George Turner, 17-Jamie Bhati, 18-WP Nel, 19-Glen Young, 20-Jack Dempsey, 21-George Horne, 22-Ross Thompson, 23-Damien Hoyland.
(Writing by Mark Gleeson in Cape Town; editing by John Stonestreet)
