For Sinner, it concludes a successful season that saw him claim his first two Grand Slam titles at January’s Australian Open and September’s US Open.
The 23-year-old, who also won the season-ending ATP Finals earlier this month, has lost just six of his 76 ATP Tour matches in the last 12 months.
Speaking in a news conference after their Davis Cup triumph, Berrettini described Sinner as “the most humble guy on the planet”.
However, Sinner’s year has been disrupted by an ongoing doping controversy which has left his immediate future in the sport uncertain.
“Of course it’s in the head a little bit,” Sinner said about the doping case.
“The most important part is all the people who know me as a human being trust me — that’s why I kept playing the level I have.
“I was emotionally a bit down, a bit heartbroken. Sometimes life gives you difficulties and you just have to [deal with] it.”
Sinner looked fatigued as he was forced to a tie-break in the opening set against Griekspoor, but surged late on in the second to seal Italy’s third Davis Cup triumph on his fourth match point.
Italy become the sixth team to win back-to-back Davis Cup titles since the final stage was introduced 52 years ago, and first since the Czech Republic in 2013.
