Root ranks century his best to date

Joe Root picked the perfect time and place to score his first Test hundred since last year's Ashes series against Australia.

The 24-year-old had not reached three figures in Tests since hitting 130 at Trent Bridge last August, an innings that hammered home England's advantage following Stuart Broad's demolition job on Australia's batting line-up on the first morning in Nottingham.

You don't need me to remind you about Broad's barely-believable haul of 8-15. 

WATCH: Broad rips through Australia

But Root's innings was his second major contribution during a series that had seen England ambush the Australians in the opening Test at Cardiff and then wrestle back the momentum following their pitiful defeat at Lord's.

Root's 134 at Sophia Gardens was thanks in large part to the life he was given early in his innings by wicketkeeper Brad Haddin.

He ensured the Australian would go on to regret that slip in what was probably the key passage of play in the whole series. 

WATCH: Root hits triple figures against Australia

The Ashes, though, was a rarity for Root, who failed to convert 10 of his 13 fifty-plus Test scores in 2015.

He broke that frustrating habit on day two of this third Test against South Africa to help rescue England from a precarious 4-91 midway through the afternoon session.

By the close, Alastair Cook's men had rallied to 5-238, just 75 behind South Africa's first-innings 313 and with the prospect of a handy lead now in the offing.

Root's knock here was arguably his finest century so far in his burgeoning international career.

Yes, those Ashes knocks last year were good but this innings was in tough conditions against a pumped-up bowling attack who had scented blood after the early wobble that had seen Alex Hales, Cook, Nick Compton and James Taylor all fall cheaply.

Asked if this effort would outrank even those match-defining contributions against Australia, Root, who will resume on 106 on day three at The Wanderers, said: "Yes. But we're going to have to do a lot of hard work to get a positive result and the rest of this innings is going to be crucial. 

"We'll have to build some strong partnerships if we want to get a lead. If we can do that we can put South Africa under pressure."

Ben Stokes played his part again yesterday, putting on 111 with Root in 95 balls as he followed up last week's breathless double hundred in Cape Town with 58 in 54 balls here.

"He takes pressure off you at the other end when he comes in and plays that aggressively," said Root. 

Quick Single: Root helps put England in control

"Hopefully he can continue the great form he's in on the rest of this trip.

"When you see someone scoring at the other end like that and putting the bowlers under pressure it brings that out in your own game as well. It's nice to have that. 

"He scored at over a run-a-ball today and in the match scenario that was really important for us. The quicker we can score the better chance we have of getting a positive result in this game."

As for his own innings, finally getting over that annoying habit that had seen him pass up countless chances to add to his Test century count – now at nine – Root said: "There was quite a lot of relief when I managed to get past three figures. Unfortunately I've not managed to do that recently. So now's the time to push on and make a big one."

England will hope he can do just that to ensure there is no way back in the series for South Africa. 

A win here will see Cook's men, already 1-0 up, take the series. 

With Root in this kind of form that now appears the most likely outcome.