Smith finished with eight birdies while his Ripper GC teammate Leishman also sank eight birdies, but bogeyed the third hole.
The closing holes at Centurion Golf Club were there for the taking.
Leishman birdied five of the last six holes, but that came at the beginning of his round because of the shotgun start. Leishman began his round on the 12th hole.
LIV Golf-London is where the Saudi-backed league began last year, when South African Charl Schwartzel took home the title.
For Smith, this is the last tournament he plays before defending his title in the British Open, to be played July 20-23 at Royal Liverpool.
"It was just really good," Smith said of his round. "Wasn't much bad stuff in there, to be honest.
"Probably got a little bit scratchy there through the end of the tough bit of that front nine, but I don't really put that down to really poor swings, kind of just mental errors.
"But left them in pretty good spots anyway. All in all, yeah, really solid."
Smith and Leishman play for Ripper, which led the team scoring after one day.
"Yeah, happy with the day," said Leishman. "I didn't do too much wrong. Pretty tough stretch from sort of 1 through to about 7 I would say and played them really well with only one bogey and a couple of birdies.
"Yeah, happy to get out of there with a 7-under and a good start to the tournament."
Thomas Pieters had a 66 and was in third place. Talor Gooch, who leads the LIV Golf points list, was among those at 67.
PGA champion Brooks Koepka started and finished his round with a bogey and shot 72, leaving him in a tie for 33rd.
Koepka this week unloaded on his Smash teammate Matthew Wolff, accusing him of quitting on rounds and wasting talent.
Wolff had only two birdies in his round of 73 and was tied for 38th in the 48-man field.
with Reuters
