The Australian caused a huge upset at Arthur Ashe Stadium, beating an uncharacteristically poor Federer 3-6 7-5 7-6 (9-7) 7-6 (7-3). My dad died when I was young, so I got away with a fair bit from my mum.
To his credit, Millman the World No 55, competed like an athlete on a mission.
Next up for the Australian is a quarter-final match-up against sixth seed Novak Djokovic.
It's the first time Millman has defeated a top-10 opponent, but Federer has always been a big supporter of his opponent.
The Swiss tennis legend made plenty of unforced errors in the marathon match, so Millman acted as humbly as he could in victory. But today he was definitely not at his best.
Millman has a secret party trick up his sleeve: tying a knot in his mouth.
They have played just once, with Djokovic winning 6-2, 6-1 in the round of 32 at Queen's Club in June.
Both Nishikori and Djokovic missed last year's US Open with arm injuries.
He's been on tour paying his dues since 2006. At one point he almost quit tennis because of various injuries that required more than one shoulder surgery and a groin surgery.
"With that you have to start all over again".
"It's challenging financially. It's challenging physically. It's challenging physically. It's challenging mentally", Millman said.
"So, you know, move on and take a rest".
"But it makes you really appreciate these moments even more". "But [I'm] enjoying playing every match and enjoying playing tennis again a little more than before".
Millman cracked the Top 50 for the first time in his career in July.
Millman has struck 72 winners to 140 from that of Federer, Mikhail Kukushkin and Fabio Fognini combined. I'll obviously remember this for a long, long time.
'When you feel like that, everything is off.
"I'm under no illusions that I'm going to have to have one of my very best days to get the job done".
The Brisbane native was invited to practice with Federer earlier this summer. He was manipulating me around the court, " Millman said. "Then I come back for the Laver Cup (in Chicago) and hopefully finish the year strong". The internet was still abuzz, before the Swiss could even walk out on court, about that around-the-netpost shot he - nearly casually - played against the talented Nick Kyrgios at the same venue a few days earlier. He hit 10 double faults and only landed six of 24 first serves in play during a marathon opening game at the start of the second set.
Said Millman: "Roger's a hero of mine". I'm not saying that it's imminent but he may feel "look, I've had enough". And I've seen that flippant tweet more times than I care to remember as he went on to win another three Grand Slam titles. "But it's really important when someone does have an off day that you capitalize, and he's probably one of the guys it's toughest to do so against".
WATCH the US Open from the quarter-finals onwards LIVE, FREE and in HD on SBS or streamed live via SBS Sport and SBS On Demand.