It rockets in at about 200 kilometres an hour, with a hellacious, ball-fluffing kick that can carry it to head height on a tall man.
And that's Milos Raonic's second, weaker serve.
Raonic is justly famous for his first-serve screamers, but Plan B isn't exactly a lesser peril – as Nikala Scholtz of South Africa found out in his Davis Cup encounter Friday with the big Canadian.
Down 0-15 and 4-3 in the second set, Scholtz wound up a backhand return as the ball sailed over the net.
He whiffed on it completely.
"The biggest serve I've ever played against, and might even ever play against," the 21-year-old University of Mississippi sophomore said after match, won by Raonic in three sets, 7-5, 6-4, 7-5.
If all you do is glance at the scoreline, it was a closer-than-it-should-have-been match between players who have similar games (big serve, big forehand).
The reality is different.
The 21-year-old Raonic was a little gloomy at not having dominated an opponent who has no professional ranking (and more than a little miffed at the chair umpire over a contentious call in the second set), but he wasn't pushed anywhere close to the edge.
"I was holding points pretty comfortably, I'm a little disappointed I didn't have more break opportunities early," the Canadian said, adding: "I'm glad I won, but not necessarily happy with the way I played."
He can, however, be happy with the way he served.
The 15th-ranked men's player in the world won 51 of 52 first-serve points, 17 of 28 second-serve points, and gave up precisely zero break opportunities; he also cannoned 26 aces past Scholtz.
And as a result, his country is in control of the World Group playoff, up 2-0 after the singles matches in which Raonic and 22-year-old teammate Vasek Pospisil chalked up straight-set victories.
"It was a good day at the office," Canadian captain Martin Laurendeau said with a smile.
It's not hard to see why John-Laffnie de Jager thinks Canada is the best Davis Cup team he has faced since becoming South Africa's captain in 2005.
"You guys [Canada] are in a good position, man," he said.
That's true both in a meta sense – given the relative youth of this country's players and in relation to this weekend's tie.
Though de Jager correctly pointed out that it's eminently possible to overcome an 0-2 deficit in Davis Cup – "It's happened to us," he noted wryly – the South Africans are heavily overmatched.
On Saturday, Raven Klaasen and Izak van de Merwe face the Canadian tandem of Pospisil and Daniel Nestor, who has merely spent most of the last decade as the No. 1 doubles player in the world (he sits third in this week's rankings).
Should Canada triumph, it will win the tie. A South African victory will add suspense to the two final singles matches on Sunday.
Don't bet against the Canadians in doubles, however.
Pospisil clearly revels in the international team competition. "I feel like I want to win a lot more in Davis Cup than when I play for myself," he said with a laugh – and the 40-year-old Nestor is showing few signs of slowing down.
Nestor's experience should be a key factor this weekend, but also for the road ahead.
Should Canada beat South Africa – a team playing without its two top players because of withdrawals and injury – the squad will remain in the elite World Group, and the ambition is to win a tie at the highest level in 2013.
But there is some work to be done before that can happen. And while Laurendeau was pleased with having the lead, he said: "We can't let them get back into this, we need to get this done [Saturday]."
In Friday's opening match, Pospisil chalked up a 6-3, 6-4, 6-4 win over van de Merwe (118th in the ATP ratings).
Ranked 116th after a summer in which he reached as high as 85th, Pospisil survived a shaky first serve – he landed only 51 per cent of them – to open the tie with a confidence-boosting win.
"I really wanted to win, get that first match – hopefully, now the team can build on this momentum," the tall right-hander said.