Max Verstappen was "typical" in his relentless hunt of Charles Leclerc for the Emilia Romagna Grand Prix sprint victory, according to Nico Rosberg.
From pole position, the reigning F1 champion lost out to title rival Leclerc at the start after struggling to get off the line, with the Ferrari holding a comfortable margin over Verstappen throughout the event until late on.
With two laps remaining, Verstappen made the most of Leclerc's troubles with left-front tyre graining around Imola to reel in the deficit and deliver a superb overtake around the outside of Tamburello to clinch top spot for Sunday's grand prix.
Speaking to Sky Sports F1, 2016 champion Rosberg said: "It certainly is quite a worry for Ferrari because the tyre deg was very big at the end there.
"The lap time difference between the two was quite significant so that is not going to make it easy for them tomorrow.
"Verstappen, just typical, so relentless. It is like he is one of those guys you least want to see in your mirrors getting bigger and bigger because you know that guy is going to attack, giving it 100 per cent.
"That is what he did again with a brilliant move which was fantastic to see."
It was the first sprint event after last year's three trial weekends, with action taking place throughout the field at a circuit where it has been historically difficult to overtake.
"I am loving these sprint races, to be honest," insisted Rosberg. "It was really fun to watch, really good action and I am all for it."