Finn on form as England push on
England finished on top on the first day of the third Test as - after enduring a sluggish start - they claimed seven wickets for South Africa's 267 runs at the Wanderers.
The hosts suffered a chaotic morning when wicketkeeper Quinton de Kock was ruled out with a knee injury and replacement Dane Vilas was hastily flown from Port Elizabeth to Johannesburg, but soon settled once AB de Villiers won the toss.
South Africa batted first and put on 73 runs before lunch for the loss of Stiaan van Zyl.
But England, with a handful of players seemingly suffering from the sickness bug affecting their camp, battled back.
Moeen Ali removed Dean Elgar for 46 and Steven Finn unpicked former captain Hashim Amla (40) with a beauty to restore the balance.
While De Kock's unexpected absence caused South Africa a headache in the morning, England had their own issues.
Alex Hales was passed fit to play after suffering viral symptoms but Alastair Cook joked that some of his side were "trying to climb out of their death beds".
With clouds overhead and a couple of awkward deliveries from James Anderson and Stuart Broad at the start of their spells, it looked a decent toss to lose.
But the trail went cold quickly.
The seamers allowed too many balls to pass through without a shot offered and after an hour's play South Africa had moved along to 40 without loss.
By then there had also been a first over of spin from Moeen and a testing start from Finn, who found a better line.
But it was England's golden boy Ben Stokes who drew first blood, removing Van Zyl for 21 with his third delivery.
This was pure batsman error though, Van Zyl shaping to pull from a poor position, changing his mind and chipping a top edge tamely into Jonny Bairstow's gloves.
Elgar and Amla added 29 before the break, but Finn beat the latter with a cracker from the final ball of the session.
And Finn deserves to share top billing with England's feted new ball pairing, according to bowling coach Ottis Gibson at stumps.
For several years England's attack has been built around the established duo of James Anderson and Stuart Broad, who have shared the load during some of the country's finest recent triumphs on their way to a combined 750 Test scalps.
But Finn comfortably outshone both senior men and figures of two for 50 scarcely did the 6ft 7in seamer justice as the Proteas made 267 for seven.
But Gibson knows just what an asset the 26-year-old is.
"I'm very impressed with Finn, since he came back in the team in the Ashes he has certainly proven himself to be an outstanding fast bowler," he said of the series' top wicket-taker.
"Often a lot is said about Broad and Anderson, and they're quality bowlers with 700-odd wickets between them, but when Finn has the ball in his hand he looks a quality bowler as well.
"He's someone you can see playing a huge part for England in the coming years."
Finn shared the second new ball with Anderson in the evening session, though Broad's demotion may have owed as much to him feeling off-colour as anything else.
Gibson was satisfied with the position at stumps, despite a late unbroken stand of 42 between Chris Morris and Kagiso Rabada.
"Sometimes when the ball is doing a bit you think you should bowl the opposition out but you've got to remember they're in home conditions and they're good players," he said.
"To have them seven down on the first day of a Test match away from home is quite pleasing."