The left-handed Californian Tien soaked up the applause at Margaret Court Arena after the biggest win of his young career following four hours and 48 minutes of seesawing action.
The feisty Russian, a three-time finalist in Melbourne, lost his cool in the third set before rallying to beat unheralded Thai Kasidit Samrej 6-2, 4-6, 3-6, 6-1, 6-2 on Rod Laver Arena.
Medvedev still leads their head-to-head 7-6, although the Italian Sinner has won six of their last seven meetings.
Top seed Swiatek, who won the title two years ago, showcased her all-court game in a straightforward 6-4, 6-1 win over Russian Liudmila Samsonova to open the evening session at Arthur Ashe Stadium and warned she was only going to improve.
The Russian looked out of sorts early on Centre Court as he lost the first set.
Medvedev, a semi-finalist last year, hit 16 aces in his 6-3, 6-4, 6-2 win over Aleksandar Kovacevic of the United States.
De Minaur had never got past the second round at the tournament before this year, winning just three of 10 matches.
Italy's Jannik Sinner destroyed defending champion Daniil Medvedev 6-1, 6-2 in just 69 minutes on Friday to reach the final of the ATP Miami Open, where he will take on Grigor Dimitrov.
Daniil Medvedev returned to action for the first time since his Australian final defeat on Tuesday with a straight sets win over Alexander Shevchenko in Dubai.
Since Stan Wawrinka won his only title in Melbourne in 2014, Novak Djokovic has picked up six trophies, Roger Federer has won two and Rafael Nadal has won one.
Jannik Sinner ended defending champion Novak Djokovic's bid for a record 25th Grand Slam title on Friday, snapping the Serb's astonishing 33-match winning run at Melbourne Park to reach his first major final.
Former US Open champion Medvedev will hope to get third time lucky when he meets Italian youngster Jannik Sinner on Sunday
Third seed Daniil Medvedev was forced to dig deep into his reserves to outlast Hubert Hurkacz 7-6(4), 2-6, 6-3, 5-7, 6-4 in the tightest of quarterfinals on Wednesday and reach the last four of the Australian Open for third time.
The key difference was the unforced error count, with Borges making 66 to Medvedev's 34
A change of racket helped Daniil Medvedev come from two sets down and prevail over Finland's Emil Ruusuvuori at the Australian Open on Thursday in a battle that stretched four hours and 21 minutes.
"The conditions were brutal," said Medvedev. "The more he (Atmane) plays this intensity, the better he will be prepared."
The 36-year-old from Serbia defeated Stefanos Tsitsipas in last year's final for a record-extending 10th Melbourne crown then added the French and US Open titles to his collection in 2023.
He reads his opponents like a book and then translates the lessons onto the court.
Novak Djokovic defeated Daniil Medvedev in straight sets on Sunday to win his fourth US Open and a record-equalling 24th Grand Slam singles title, cementing his claim as the greatest tennis player in history.
