The England coach had sprung a shock by picking Smith ahead of Freddie Steward in the number 15 shirt for the crunch Fiji clash, the selection of the Harlequins back leading many to believe that a more attacking style of play might be on the cards.
Steward had started 29 of the 30 Tests since his debut in 2021, valued at the back for his superb aerial and defensive game.
Smith is a more attack-minded playmaker, but it was just his second start in the No 15 jersey after he took a starring role in the 71-0 pool demolition of Chile.
A hard-hitting Fiji were a different prospect from the South Americans, however, proving tough to break down as England got dragged into a dogfight where breakdown superiority was more salient than flowing ball-in-hand play.
In a tight, forwards-dominated match at the Stade Velodrome where defence was king, Smith showed a safe pair of hands to field the opening Fijian kick clearance.
He then fell into the first receiver role and half-jinked his way through the defensive line to whet the appetite of what might be to come.
It was short-lived as the packs went toe-to-toe.
Smith's first attempt at a tackle saw Fijian winger Semi Radradra bounce him out of the way before a scrambling English defence arrived to snuff out the attack.
A one-handed show and attempted go ended in a turnover for Fiji and what should have been a penalty, Frank Lomani's kick coming back off the post.
In the 23rd minute, Smith was left dazed after Vinaya Habosi clashed heads in a clumsy tackle that earned the Fiji winger a yellow card.
Smith had to leave the pitch for a head injury assessment, with Elliot Daly falling into the full-back slot from the left wing.
Winning his 29th cap, he was again railroaded by Radradra as Fiji fought back into the match, leaving him with a gashed head.
Attacking opportunities became even scarcer as the Pacific Islanders rallied and it was left to sharp-shooting stalwart Owen Farrell, preferred at fly-half to George Ford, to drop a goal to pull England away to 27-24 and then boot a fifth penalty with three minutes to go to ensure the victory.
Farrell's 20-point haul took the Saracens fly-half to 1,201 points, having already broken Jonny Wilkinson's previous England points record of 1,179 during the narrow 18-17 win over Samoa in their final pool match.
While Farrell was unerring with the boot, bar one conversion that came back off the post, the creativity offered in midfield was limited and England had to rely on two moments of individual brilliance from centres Manu Tuilagi and Joe Marchant for their tries.
Farrell was lucky not to end the game in the sin-bin after a deliberate knock-on as Fiji pushed in a thrilling climax. He instead dusted himself down to collect the man-of-the-match award and England head into the last four.
