The 25-year-old Brazilian Thiago Monteiro will compete in the first ATP quarter-final since Hamburg 2018, stunning the 4th seed Borna Coric 6-4, 7-6 in an hour and 45 minutes. Borna is yet to find his rhythm in 2020 and Buenos Aires will not be the event to do so, losing serve twice and stealing Monteiro's serve just once to hit the exit door on tournament debut.
It was an intense battle from start to finish, with servers as the main actors almost all the time, offering the returners no break chances in the second set that was decided with a late mini-break from Thiago in the tie break, the one that sent him into the last eight.
The start didn't look like that at all, with three breaks of serve in the opening five games, two for the Brazilian who grabbed an early lead against the better-ranked opponent. Monteiro netted a backhand in the second game to fall behind, pulling it back in the next game and opening a 3-2 advantage with another break in game five after an error from Coric at the net.
Settling into an excellent rhythm following that early break he experienced, Thiago barely lost a point behind the initial shot, sealing the first set with a service winner in game ten for a 6-4. As we already said, nothing could separate them in set number two, with 12 commanding holds and 12 straight points won by servers in the tie break.
A left-hander wasted a match point at 6-5 following a terrible smash, scoring another mini-break in the next point thanks to a forehand error from Coric and moving over the top with a forehand winner, notching one of the best victories in his career so far.
The 3rd seed Dusan Lajovic had to dig deep against the Spanish qualifier Pedro Martinez, prevailing 7-6, 7-6 in two hours and seven minutes. Dusan won six points more than his opponent, fending off two set points at 4-6 in the opening set tie break and three more in the 12th game of the second set, edging the youngster 8-6 in the breaker to seal the deal in straight sets.
The 8th seed Casper Ruud had a much more relaxed day at the office, toppling Roberto Carballes Baena 6-1, 6-0 in 57 minutes to reserve the place in the quarters. The Norwegian lost ten points in seven service games, setting the bar high and dominating on the return as well to rattle off 11 straight games after five breaks on his tally.
Casper grabbed a break in the fourth game when Carballes Baena netted a backhand, producing another one at 4-1 thanks to a forehand mistake from the Spaniard and securing the opener with a hold at 15 a few minutes later for a 6-1.
There was only one player on the court in set number two as well, with Ruud moving 5-0 up after a forehand winner before holding at 15 for a bagel and a picture-perfect triumph.