Edinburgh - Scotland coach Gregor Townsend regards beating South Africa on Saturday at Murrayfield would be a bigger achievement than beating England this year.
Scotland hadn't beaten England in a decade when they pulled off an impressive win in February in the Six Nations.
The Scots haven't toppled the Springboks since 2010.
Asked where a victory this weekend would rank in his 18 months in charge so far, Townsend said on Wednesday: "Given what South Africa have done recently, it would probably be our biggest win in the last couple of years.
"England stands out as such a memorable win. The fact they had won so many games in succession and that trophy we play for makes it even more special. But I just feel that South Africa are in the top two or three teams in the world with the way they play against the best teams in the world.
"Going to New Zealand and beating them, almost beating them a second time, showing what they were capable of last week against France as they came from behind to get a great win, that all shows they are going to be a tough team to beat."
He expects an attritional Test against South Africa.
"It's the No 1 physical challenge," he said. "We get physical challenges in the Six Nations with the likes of England and France and Ireland but any coach will tell you that the biggest physical challenge is South Africa. It always has been.
"They have evolved their game since Rassie Erasmus took over but they've not gone away from the forward pack. They select the biggest and strongest men they can find."
After beating Fiji 54-17 last weekend, Townsend made six changes, five in his pack. Prop Gordon Reid, hooker Stuart McInally, locks Jonny Gray and Ben Toolis, and flanker Hamish Watson were back. Sam Skinner starts on the blindside flank where he finished the Fiji Test, having made his debut at lock.
Huw Jones was trusted with a recall at centre despite a couple of defensive slips in Cardiff against Wales.
Only prop WP Nel, loose forward Ryan Wilson and wing Tommy Seymour, who scored a hat-trick of tries against Fiji, are starting a third consecutive Test this month.
15 Stuart Hogg, 14 Tommy Seymour, 13 Huw Jones, 12 Pete Horne, 11 Sean Maitland, 10 Finn Russell, 9 Greig Laidlaw (captain), 8 Ryan Wilson, 7 Hamish Watson, 6 Sam Skinner 5 Jonny Gray, 4 Ben Toolis, 3 WP Nel, 2 Stuart McInally, 1 Gordon Reid
Substitutes: 16 Fraser Brown, 17 Allan Dell, 18 Simon Berghan, 19 Josh Strauss, 20 Jamie Ritchie, 21 Ali Price, 22 Adam Hastings, 23 Chris Harris.