Fellow paceman James Anderson (3-58) also took a trio of scalps at Lord’s, including opposition captain Graeme Smith, as England reduced the tourists to 54-4 early in a match they must win to retain their No1 Test ranking.
Duminy (61) and Vernon Philander (46 not out) got South Africa back on track and helped steer them to 262-7 at the close, as England attempted to prove they could compete without axed batsman Pietersen.
His text messages to Proteas players disparaging his own skipper have made him a pariah and plunged his international future into huge doubt, but Finn insisted the players had ignored the storm.
“What’s happened hasn’t affected the way we’ve approached this game. I thought we were great as a team out there today, as 11 people out there on the pitch,” said Finn.
“Whenever we go and bowl, regardless of what’s happening elsewhere, we always want to do what we do well. Even if what happened in the last week hadn’t happened, we’d still have gone out there and had the same intentions.
“Bowling first, there’s always a bit of pressure to take early wickets. I thought we bowled beautifully in the first session. As the day went on the ball got a bit softer, the wicket didn’t have as much zip, but I thought we stuck to our guns really well.”
England’s attempts to avoid a first home series defeat for four years were aided by the television umpire, whose controversial decision to give Jacques Kallis out bemused, and significantly dented, South Africa.
“It’s one of those things we can’t comment on, but we were a little disappointed,” said Duminy. “You win some, and you lose some. England are more on top, but we are happy with the fighting spirit that we showed.”