Jantjies came on for the injured Lambie during the 26-20 first test defeat at Newlands on Saturday but coach Allister Coetzee seemed to suggest afterwards that the replacement pivot had not stuck to the tactics.
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Yet Whiteley, who plays with Jantjies at Super Rugby front-runners Lions, said he was confident the 25-year-old would be able to help engineer a Springbok comeback. "Elton could play to any plan," Whiteley, who played as a second-half substitute, told reporters.
"I've played so many games with him, I can tell you he's a tactically intelligent player. He's someone who attacks the line flat and you could see that last night. He was asking questions of the defence.
"But he can also put the ball in behind them and we've seen that in Super Rugby numerous times with his cross kicks and his little kicks in behind. He's a very smart player."
Lambie will sit out the second test but could be back for the third, South African officials confirmed on Sunday.
Coetzee revealed the Boks' plan had been to kick into space behind a rushing Irish defence but after Lambie was concussed in a tackle by Irish flanker CJ Stander it was rarely carried out.
"I think we were a bit naive, tactically. The second opportunity (to kick in behind the defence) was when Patrick Lambie got tackled.
"He saw that space, but we didn't do it again. The space was given by the Irish out wide and then we weren't clinical. If we could fix those little things I think we could improve."
(Editing by Ian Chadband)
