Gregor Townsend has admitted he waited too long to use his replacements in Scotland's 42-28 defeat to South Africa in Pretoria on Saturday, as the Springboks completed a clean sweep of Six Nations and Rugby Championship nations over the past calendar year and stretched their winning run to ten straight Tests.

Scotland were level at 14-all at half-time and troubled the Boks throughout, but tries from Elrigh Louw, Damian Willemse and Zach Porthen opened a 35-14 gap before Josh Bayliss and Ben White gave the visitors late hope. Jesse Kriel's try in the 77th minute closed out the win.

Townsend credited his finishers for the comeback momentum but acknowledged they should have been introduced earlier. "The starters put in a huge effort but the bench were the ones making those line breaks and finishing off opportunities," he said. "Perhaps we could have got the bench on earlier – easy in hindsight, but they certainly made a big, big impact when they came on."

Asked directly whether South Africa deserve their world number one ranking, Townsend was unequivocal. "Yes. They showed it again today. They've obviously got huge strength and depth. They won a number of games in November when they were down to 14 men, and they found a way to win today."

Rassie Erasmus used the match deliberately to assess fringe squad members against high-calibre opposition, indicating Scotland presented a stiffer examination than England. "Sometimes we must put our personal goals to one side – how many games you've won in a row or even putting winning this championship on the line – so that you can know who can do what," Erasmus said. "If you don't make those calls you would never know." It was Scotland's first Test in South Africa since 2013.