Calcutta: Mitchell Johnson, who struck terror in the hearts of best batsmen of the world, feels South African AB de Villiers is a class apart. Johnson, who retired from all forms of international cricket on Tuesday, said that de Villiers was the hardest batsman to crack, during his 73-Test career in the Baggy Green.

"AB de Villiers, he's one outstanding player of our generation," Johnson told Inside Cricket, Cricket Australia quoted in its website. "He was always so difficult to get out and a huge challenge. I remember the game at Centurion (in 2014) and I'd got a few quick wickets in that game and he came out to bat and looked so calm and composed and just played his natural game.

"It really is difficult when someone does come out like that and you're on top of your game. But it really is a great challenge and he's been one of the best players I've played against."

In that Centurion Test, Johnson claimed 12 wickets and the Man of the Match award, ripping apart the Proteas with the same pace and hostility that destroyed England in the Ashes only months earlier. And while Johnson dismissed de Villiers twice in that match, the prodigious right-hander cut a lone figure for the humbled hosts, top-scoring in both innings with 91 and 48.

Former Australia teammate Shane Watson recalls Johnson's ferocious spell at SuperSport Park, from the sidelines, and was taken aback by how easily de Villiers handled a rampant Johnson at the peak of his powers. "You've got world-class players of fast bowling and jeez, Mitch was incredible," Watson told a website.

"Even though when AB de Villiers came into bat, it was like Mitch was bowling 110kph, but that's a different story. For all the other normal people ... it was incredible to watch."

Johnson dismissed de Villiers five times in the five-day format and three times in one-dayers since they first collided in December 2008. De Villiers was ranked the 10th greatest player of the 21st century by this website earlier this year, while Johnson's prolific career saw him finish in 22nd spot.

Johnson said the passing of Phillip Hughes led him to question his aggressive approach to the game. Johnson terrorised English batsmen in the 2013-14 Ashes campaign with a barrage of short-pitched bowling, a year before the entire sport was rattled after Hughes was fatally struck by a bouncer during a Sheffield Shield match late last year.

"It still hurts to this day," Johnson said. "It definitely affected players around the world and I think it changed the game a little bit for a while there. I had that Ashes series where I was really aggressive and bowling a lot of short balls and I did hit players. And it made me think, was I doing the right thing? You know, was I playing in the spirit of the game? Eventually, Johnson concluded the short-pitched delivery still had its place in the game.

The left-armer was never at his destructive best again following that watershed 2013-14 season, in which he took 58 wickets in eight Tests against England and South Africa at an average of 15.50.