London, United Kingdom: Joe Root said he had finished his first day as England captain in "dreamworld" after making an unbeaten 184 in the first Test against South Africa at Lord's on Thursday.

Root did not have much of a voice to use at his post-play press conference after waking up feeling "pretty groggy".

But opting for an old-fashioned approach of wearing several layers trying to sweat out his cold while taking on plenty of fluids, he helped England turn the tide on the opening day of this four-match series.

They were 17 for two when the 26-year-old Yorkshireman came to the crease and 76 for four before lunch, with seamer Vernon Philander taking three wickets.

Yet by stumps, England had recovered to 357 for five, justifying Root's decision to bat first after winning the toss.  

Root, who was aided by Ben Stokes (56) and Moeen Ali (61 not out) in successive century stands, admitted luck had gone his way.

He had managed just five when he mishooked Kagiso Rabada, only for the ball to fly over the head of Aiden Markram after the substitute fielder had made the mistake of not being right back on the rope at long leg.

Further good fortune for Root followed when he was dropped in the gully on 16 off the luckless Rabada and again on 149 when he was stumped by yards off Keshav Maharaj only for the spinner to have over-stepped -- the second time in the day that an avoidable no-ball cost the Proteas a wicket.

- 'Fall into place' -

Root told Sky Sports he had felt "in a bit of a dreamworld" and later, talking to reporters, he accepted he could hardly have written a better script for himself.

"I don't think so, especially getting dropped once and just chipping someone on the boundary. It just seemed to fall into place today," he said.

"When you get a life early, sometimes you feel like it is your day and you've got to try to make the most of it."

Root added: "I felt pretty groggy this morning. But nothing was going to stop me enjoying the day.

"I made the most of everything and the cold wasn't going to get in the way.

"It may have helped me concentrate slightly out there, knowing I wasn't a hundred percent."

He now has the chance to surpass the previous highest score in a first Test as captain of 239 made by New Zealand's Graham Dowling in 1968.

"It was a nice feeling getting that call back (after the over-turned stumping) when you know you've made a glaring error like that," said Root, who added he would look to push on to a "really big score".

In the morning it was Dean Elgar, leading South Africa for the first time while Faf du Plessis remains at home with his wife after the birth of their first child, who was on course for a dream day.

"He couldn't put a foot wrong up till lunch and then everything went pear-shaped after," said Philander of his stand-in skipper.

Philander added the team had let Elgar down, especially in conceding 13 no-ball runs.

"There's probably no excuse for that," said the bowler, who bowled three no-balls.

"A couple of guys overstepped and cost us a couple of wickets.

"He (Root) gave us chances and, if we're honest with ourselves, if we'd taken one of them we could have bowled them out for under 200.

"But he took his chances -- very well-batted to him," Philander added.