The American, who celebrated his 24th birthday by defeating Tommy Paul on Thursday, rallied from a break down in the first set and won 73 per cent (19/26) of his first-serve points to advance after 74 minutes.
“It feels great. I came out and played really well today,” Fritz said in his on-court interview. “I knew what I had to do and I did it and I played well and I am happy to be in the semi-finals. There was a really important point [at the start of the second set] and I won that point and I carried the momentum from there. It was a really important break.”
FOLLOW THIS WEEK’S ACTION
Fritz is yet to drop a set in St. Petersburg and arrived at the ATP 250 event in form, having defeated World No. 4 Alexander Zverev en route to his first ATP Masters 1000 semi-final in Indian Wells earlier this month.
The fifth seed now leads Millman 2-0 in their ATP Head2Head series and will face second-seeded Canadian Denis Shapovalov or German Jan-Lennard Struff in the last four. It will be Fritz’s sixth tour-level semi-final of the season, with the World No. 28 also advancing to this stage in Doha, Cagliari, Los Cabos and Atlanta.