But 3 hours, 34 minutes later, Murray was gone, a stunning upset victim to the unseeded German 7-5, 5-7, 6-2, 6-4. For Zverev, a journeyman who has overcome a long history of injuries, the match had to feel longer than those three-and-a-half hours.
How did he win the match of his life?
"Honestly, I don't know," he said in his on-court interview. "I was in a little coma, serving and volleying. There were a few points that I don't know how I did it."
"Just wasn't meant to be," a disconsolate Murray said afterward. "[Zverev] served very well when he needed to, especially when he was behind in games. Yeah, he deserved to win because he played great when he was down and also in the important moments."
"Obviously, it's a tough one to lose," Murray said. "Obviously, I wanted to go far in this event. It's the earliest I've lost here for, I don't know, a long time, so I'm disappointed right now. Credit to him. He came up with great, great shots and played a really, really good match."
Zverev, the 29-year-old brother of rising star Alexander Zverev, is an extremely unorthodox player, a left-hander who serves and volleys like the Aussie players of the 1970s.
The crowd at Rod Laver Arena quickly got behind the 50th-ranked Zverev, who -- aside from one badly butchered overhead -- never really lost his nerve. He broke Murray's serve eight times in 21 tries.
Although Murray and Zverev had met only once at the ATP level, their history goes back to juniors. Murray won all three of their matches, beginning with an F10 Futures event in Glasgow, Scotland, in 2003, when they were 16, marking Murray's first professional title, played in the city in which he was born. Later, he prevailed in the semifinals of the US Open juniors (2004) and an Italian F8 Futures in 2005.
The shocking defeat brings a series of statistics into play:
• The last time the top two seeds on the men's side failed to reach the quarterfinals of a major? The 2004 French Open, in which Federer and Andy Roddick were stopped short.
• The last time Murray and Djokovic both failed to reach the quarters at a major? Here, in 2007.
• The last time Murray lost to a player ranked this low at a Grand Slam? In 2006, when he fell here to Juan Ignacio Chela.
Zverev is the lowest-ranked player to beat a No. 1 seed at a major since No. 86 Marat Safin defeated Roddick here in 2004. Always aggressive, Zverev came to the net 118 times and won 65 of those points -- a sturdy 55 win percentage.
A year ago, Zverev was ranked No. 171 in the world, a long way from automatically qualifying for Grand Slams. Now he's looking to break into the top 40 for the first time. He is into the first major quarterfinal of his career and awaits Federer, who defeated No. 5 seed Kei Nishikori.
"It means the world to me," Zverev said. "It's just amazing. I don't know yet how I feel because everything is new to me, and everything feels a little bit unreal."
Who is the favorite now? Look no further than No. 4 seed Wawrinka, who defeated Andreas Seppi 7-6 (2), 7-6 (4), 7-6 (4).
Wawrinka, a three-time Grand Slam singles winner, including last year's US Open, will play No. 12 seed Jo-Wilfried Tsonga in the quarterfinals.