Coric, who entered the tournament ranked 152nd, completed his giant-killing spree by beating Stefanos Tsitsipas 7-6(0), 6-2 in the final. He thus became the lowest-ranked Masters 1000 champion ever.
Garcia, meanwhile, won her third WTA 1000 title by beating Petra Kvitova 6-2, 6-4. Rajeev Ram and Joe Salisbury won the men's doubles title, while Lyudmyla Kichenok and Jelena Ostapenko lifted the women's doubles trophy.
Here's a look at what happened in the world of tennis this past week:
Borna Coric wins maiden Masters 1000 title in Cincinnati
Borna Coric's dream week in Cincinnati concluded with him lifting the Rookwood Cup. The Croat beat the likes of Rafael Nadal, Felix Auger-Aliassime and Stefanos Tsitsipas en route to the title.
Tsitsipas started Sunday's final on a strong note by breaking Coric early and racing to a 3-0 lead. However, the 25-year-old broke back in the seventh game and the set went to a tie-break. Coric was dominant in the tie-break, winning it 7-0 to clinch the opening set.
Borna Coric was 40-0 down in the opening game of the second set but won five points in a row to hold serve. After a few tight games, the Croat secured a crucial break in the sixth game to go 4-2 up.
He broke Tsitsipas in the eighth game as well to take the second set and the title.
It was a very special victory for Borna Coric, who has suffered with injuries over the past few years. As a result of his performances in Cincinnati, the Croat climbed a whopping 123 spots to 29th in the rankings.
Caroline Garcia wins 3rd WTA 1000 title in Cincinnati
The women's singles tournament at the Western & Southern Open also witnessed a fairy tale in Caroline Garcia's run to the title. The Frenchwoman had to qualify for the main draw of the competition and beat the likes of Maria Sakkari, Jessica Pegula and Aryna Sabalenka to reach the final.
Up against Petra Kvitova in the title match, Garcia could not have asked for a better start as she broke the Czech twice to lead 4-0. No further breaks were made and Garcia took the opening set 6-2.
The 28-year-old broke her opponent in the first game of the second set as well and this turned out to be decisive. Kvitova tried hard to break back and had three break points in the sixth game. However, the Frenchwoman managed to save them all and hold her serve.
Garcia won the second set 6-4 and claimed her third WTA 1000 title, having won two in 2017 (Wuhan and Beijing). As a result, her ranking rose from 35th to 17th.