Often utilised as a teammate for higher-profile riders on his Mitchelton-Scott team, Smith had showed strong form with a ninth-place finish at Milano-Torino three days earlier, and was ecstatic to deliver when handed the leadership.
"I'm super happy - the team were awesome. They put full faith in me and I was pretty nervous coming into the race, one of the first times the team has ridden for me and in such a big race as well. I'm just happy I can pull a result off mainly for them and the team."
It looked as if the leading duo could be caught in the final metres, and Smith described the curious and tactical nature of the finish.
"The sprint was strange, there were a few fast guys there, obviously faster than me so I had to play it a little bit smart. I just thought 'if in doubt, lead it out' - I maybe went a little bit too early, but I just put my head down.
"I managed to get around [Philippe] Gilbert, but then a couple of guys came from behind. Van Aert and Alaphilippe looked pretty close, but by the time they opened their sprint up there was still a bit of a gap."
Mitchelton-Scott sports director Gene Bates was full of praise for Smith's result.
"That was absolutely sensational, we would have been extremely happy with a top 10, so to come in sixth with Dion is a victory. It was fantastic from the group, it's a very young group and they rode exceptionally well.
"The plan was to support Dion and to give him the best run possible and the guys did a great job. He had a small touchdown before the top of the Nava climb, but it didn't seem to faze him, and he was always really relaxed. We had confidence in him and he showed really great leadership."
New Zealand's best results in monuments
6th – Dion Smith (2020 Milan-San Remo)
8th - Joanne Kiesanowski (2004 Milan-San Remo)
9th - Joanne Kiesanowski (2004 Tour of Flanders)
10th – George Bennett (2018 Il Lombardia)
10th – Hayden Roulston (2010 Paris-Roubaix)
15th – Eric McKenzie (1983 Milan-San Remo)
16th – Jacinta Coleman (2000 Milan-San Remo)
19th – Julian Dean (2009 Milan-San Remo)
20th – Bruce Biddle (1974 Il Lombardia)