Zverev and Shelton tested each other in a high-quality encounter before the world number three played a near flawless tiebreak to clinch the match in little over two hours and stretch his career win-loss record over the American to 3-0.
Six-time champion Novak Djokovic has withdrawn from this year's Italian Open, organisers said on Tuesday.
Eighth seed Machac, who won gold in mixed doubles at the Paris Olympics, became the third player from his country to win an ATP 500 title, following Tomas Berdych and Radek Stepanek.
Monegasque Valentin Vacherot completed a fairytale run at the Shanghai Masters on Sunday, rallying from a set down to defeat his cousin, Frenchman Arthur Rinderknech, 4-6, 6-3, 6-3 in the final and secure his first ATP 1000 title.
The 45-year-old Bopanna's final appearance on the Tour came at the Paris Masters, where he partnered Kazakhstan's Alexander Bublik, losing in the opening round earlier this week.
Defending champion Jannik Sinner swept past Felix Auger-Aliassime 6-0, 6-2 on Thursday to reach the Cincinnati Open semi-finals, the world number one extending his hardcourt winning streak to 25 matches.
Mahesh Bhupathi entered his first final of this season. He and French partner Michael Llodra overcame a strong challenge from India's Rohan Bopanna and Rajeev Ram of the United States in the semi-finals of the Dubai Tennis Championships on Friday.
Novak Djokovic moved to the brink of his 100th tour-level title after recovering from a second-set blip to beat British qualifier Cameron Norrie 6-4, 6-7(6), 6-1 in the Geneva Open semi-finals on Friday.
Factbox on Italy's Jannik Sinner, who beat Germany's Alexander Zverev 6-3, 7-6(4), 6-3 in the Australian Open final
The 19-year-old Czech Jakub Mensik beat his childhood idol Novak Djokovic in the Miami Open final in an upset for the ages on Sunday.
The 21-year-old German upstart produced some dazzling tennis and thoroughly deserved his 7-5, 7-6 (5) win against the six-time champion in a captivating semi-final.
Sinner's retirement and world number one Alcaraz's withdrawal due to an ankle injury blows the draw wide open, with Djokovic in the hunt for a record-extending fifth title in Shanghai.
Britain's Cameron Norrie stunned world number one Carlos Alcaraz to reach the third round of the Paris Masters.
Yuki Bhambri and his American partner Robert Galloway lost to fourth seeded combine of Francisco Cabral from Portugal and Lucas Miedler from Austria in the final.
Belgian third seed Elise Mertens dug deep to save 11 match points and battle past two-time winner Ekaterina Alexandrova to reach the Libema Open final.
Dimitrov has enjoyed the best season of his career in 2017, clinching four titles overall, including his first Masters title in Cincinnati.
Japan Open: Alcaraz marches into quarterfinals, hails "best physio in the world" after overcoming ankle issues
Jeevan Nedunchezhiyan and his partner Vijay Sundar Prashanth clinched their maiden ATP title together, winning the Hangzhou Open men's doubles event, while Yuki Bhambri and his French partner Albano Olivetti finished runners-up at the Chengdu Open
Top seed Carlos Alcaraz of Spain and No. 8 seed Hubert Hurkacz of Poland will clash in the ABN Amro Open semi-finals on Saturday after both posted victories on Friday in Rotterdam, Netherlands.
'I have no idea what's happening right now, I'm not in a dream, it's just crazy. I'm just so happy with my performance these past two weeks.'
World number two Carlos Alcaraz beat seventh seed Arthur Fils 6-2, 6-4 on Saturday to advance into his third Barcelona Open final, where the Spaniard will face Denmark's Holger Rune for the title.
With world number four Ruud already assured of a semi-final berth the match was in reality a dead rubber.
This milestone underscores his longevity and commitment to the sport, especially considering the physical and mental demands of playing at the top level.
Djokovic to face World number 204 Valentin Vacherot next.
The ATP said that penalties and fines would apply for abuse or misuse of the coaching conditions and that the trial will be assessed at the end of the 2022 season for potential inclusion in future.
Greece's Tsitsipas battled back from 3-5 down in the third set to eliminate Medvedev with a 6-3, 6-7(11), 7-6(1) win to set up a showdown on Friday with Rublev for the Red Group's other semi-final spot.
Carlos Alcaraz has defended his decision to play in the lucrative Six Kings Slam exhibition event in Saudi Arabia
Rajeshwaran shown the door at Mumbai Open
Defending champions Italy moved into the Davis Cup final after a 2-0 win over Australia on Saturday as Jannik Sinner defeated Alex de Minaur in straight sets to follow up Matteo Berrettini's victory over Thanasi Kokkinakis.
Arjun Kadhe and Vijay Sundar Prashanth were beaten in the semi-finals of the Swiss Open after losing in straight sets to third seeds Albano Olivetti and Hendrik Jebens.
Sumit Nagal registered a straight-sets win over Argentine qualifier Nicolas Kicker.
Mboko saved a match point against Kazakh ninth seed Rybakina in front of adoring home support
'It's a different surface and I've not had much time to get used to this tournament so my expectations aren't that high.'
India's top-ranked tennis player Sumit Nagal was ousted by Pedro Cachin of Argentina in the pre-quarter-finals of the Braunschweig ATP Challenger, in Braunschweig, Germany, on Wednesday.
Third seed Stan Wawrinka was knocked out in the third round of the Paris Masters when he lost 6-7(2), 7-5, 7-6(3) against South African Kevin Anderson on Thursday, suffering his fourth defeat in five matches.
India's Yuki Bhambri and his French partner Albano Olivett clinched the men's doubles title at the Swiss Open ATP Tour tennis tournament with a hard-fought win over Ugo Humbert and Fabrice Martin in the final in Gstaad
The tournament's once-robust pool of around 300 line judges has been cut to 80 and they will serve as "match assistants", who support chair umpires and step in should the ELC -- powered by more than 450 cameras -- fail in any of the 18 courts in use.
Cilic, eliminated after two three-set losses, was hoping to end his year on a high in the city where his Wimbledon dream was ended in this year's final by Federer - the Croatian sobbing on court after suffering blisters.
Medvedev outlasts Zverev to reach Halle final
Jannik Sinner's dazzling winning streak ground to a halt ahead of the French Open but the world number one's top-notch return from a three-month doping ban suggests he will be the main challenger to Carlos Alcaraz in Paris.