Warren Gatland admits that even as a veteran coach he is afflicted by nerves on matchdays as he wrestles with the "agony or ecstasy" of competing in the international arena.

The British and Irish Lions boss will be racked with tension when he takes charge of Saturday's opening fixture on South African soil against the Sigma Lions in Johannesburg.

Despite having masterminded Six Nations titles and Grand Slams with Wales, as well as holding an unbeaten record from the Test series of two previous Lions tours, Gatland still buckles himself up for a jittery 80 minutes.

"I think the thing about rugby at the highest level, whether it is Lions or international rugby, is that it's agony or ecstasy. There's nothing in between.

"It is either win and celebrate afterwards, or you are in pain for a few days reflecting on a loss."

Only the Lions' most recent expedition, to New Zealand four years ago, challenged those boom or bust emotions as a drawn series against the All Blacks brought with it a feeling of hollow satisfaction.

At the time Gatland thought his successful association with the Lions had reached its conclusion, his patience snapping at having been the target of a negative campaign waged in the local media.

"I hated the tour" he said later, but as time passed he realised that, after being part of Ian McGeechan's coaching team in 2009 that saw the Springboks emerge 2-1 winners from an epic series, he was not ready to throw in the towel.

"It felt like there was unfinished business. You realise there's a massive amount of pressure and there's a lot of expectation," he said.

"I felt that on occasions when people have not agreed with decisions I've made or when the New Zealand media had a crack at me like last time and tried to unsettle me. That was another challenge.

"But when you go away and think about it you realise what you have achieved is pretty special, drawing with the world champions.

"It is pretty hard to reject an offer to come back and coach the Lions and the opportunity you have to make some special memories."

Scotland full-back Stuart Hogg leads the Lions into their clash with the weakest opposition of the nine-match itinerary at Emirates Airline Park.