Smith was on 80 not out on the fourth afternoon, his latest epic knock of the series, when he was struck in the neck by a steepling delivery from the debutant.
Smith, who had already received treatment for a nasty blow on the left forearm and fended off a lightning fast 96.1mph ball aimed at his ribs, hit the deck immediately and remained on the floor for an extended period before stumbling to his feet.
Members of both teams' medical staff attended to him and the 30-year-old was eventually persuaded to leave the pitch, despite being seemingly reluctant to do so.
Smith was applauded from the field but within 45 minutes he was back out in the middle after undergoing medical tests.
The Australian was passed fit to continue and after Peter Siddle's dismissal marched back through the Lord's Long Room in pursuit of his third century of the series.
It wasn't to be, though, as Smith added 12 before he was removed by Chris Woakes lbw on 92.