While England's new era under Root was planned and has been prepared for since the start of the year, it was only confirmed this week that South Africa will be led by opening batsman Dean Elgar at Lord's with regular skipper Faf du Plessis missing the series-opener to be at home with his wife after the birth of their first child.
The Yorkshireman shared a fifth-wicket stand of 114 with Ben Stokes (56) after Philander (three for 28) had put England in trouble at 17 for two and then 76 for four in the first Investec Test.
England will resume on 357/5 with Root (184) and Moeen Ali (61) at the crease.
Concerns had been expressed that captaincy would reduce Root's effectiveness as a batsman.
The partnership surpassed 150 as Root set a record for a debutant England Test skipper and closed on a double-century to embrace his new role in typically confident fashion, his knock featuring 26 fours and a maximum. I think this will be a very good summer for England - they will blow Windies away and maybe South Africa too.
There is something special about Test cricket: the white clothes, red ball and five long days. At the initial period, it was Vernon Philander who was the pick of the bowlers and did maximum damage by picking up three wickets.
The second England wicket was somewhat unfortunate as Keaton Jennings (8) was adjudged to be leg before to Philander but replays showed had he reviewed he would have been saved.
Rabada also had Root dropped on 16 with the scoreboard reading 59/3‚ this time by JP Duminy in the gully.
Morkel had Gary Ballance leg-before to reduce England to 49/3 inside the first hour.
England attacked spinner Keshav Maharaj, who ended the day with 0-107, and the Proteas had to use part-timers Theunis de Bruyn and Temba Bavuma in stages to shore up their bowling. "And drawing on our experience of getting millions on their bikes with our successful eight-year Sky Ride initiative, we are committed to working with the European Central Bank to help grow the game at all levels".
Suddenly a very different day, match and series appeared in front of England and in front of Joe Root.
This season he's been in great form with the bat, scoring three centuries in the County Championship with Essex and averaging 66.7 in his 10 innings, so there's no doubt he'll be full of confidence and raring to go.
Root with confirmed that Liam Dawson, Hampshire's spin-bowling all-rounder, will bat at No8 and thus Toby Roland-Jones will wait for his debut, and targeted an upturn in fortunes for a side that lost a record-equalling eight Tests a year ago to expedite Alastair Cook's resignation. He drove Morne Morkel straight back past him for four, Maharaj back over his head for six and then another four, the same way, back towards the pavilion. Root was even stumped off a no-ball on 149. He will be fine, he has shown he can play at worldwide level before and he will do it again.