French Open champion Garbiñe Muguruza competed in her first ever match in the Arthur Ashe Stadium during the night session, and for the second consecutive year, the third seed crashed out of the US Open in the second round.
Anastasija Sevastova retired from professional tennis in 2013 and returned to competitive tennis last year, nonetheless, this was her biggest scalp.
Muguruza had the chance to leave Flushing Meadows as the world number one for the first time in her career, however, Australian Open champion Angelique Kerber, and Agnieszka Radwanska will try to wrestle it away from the current world number one, Serena Williams.
Muguruza has the stronger start in the opening set
Sevastova opened the match by serving first, and both players held their first service games comfortably, however, Muguruza was trying to be aggressive in the third game of the match but unforced errors aided Sevastova to hold firm with an ace to lead 2-1 at the first changeovers.
The third seed held serve easily in the fourth game, putting Sevastova under pressure in the following game with the Latvian committing back-to-back unforced errors giving Muguruza a 0-30 advantage.
However, Sevastova was helped by more errors from the Spaniard's game to get to 30-30, however, the French Open champion created her first break point chance of the match with a good return forcing Sevastova to come to the net and commit a forced forehand error.
The inevitable shortly followed as Muguruza broke to lead 3-2 in the first set, consolidating the break, virtue of another unforced error from the Latvian's racquet.
Sevastova wasn't going to hand the Spaniard the set easily as she held to love in the follow game to keep Muguruza at bay with a slender 4-3 lead.
In the eighth game, Muguruza was struggling with her game as more errors began to creep in and at 30-30, the third seed rushed a midcourt forehand placing it into the net to hand Sevastova, her first chance to break back.
The former world number two found her first serve at a pivotal point with the world number 52 placing her backhand into the net, although Muguruza wasn't out of trouble completely, as another backhand unforced error sailed long with another break point occurring for Sevastova.
Sevastova breaks back
Once again, another unforced error was making life easier for Muguruza to hold serve, but Sevastova broke on her third break point with an eager missed backhand from Muguruza that she should have made, nonetheless, the set was poised again at 4-4.
Immediately, the former world number two didn't let that bother her as she re-established the break to lead 5-4, and served for the opening set.
The Spaniard had the perfect start to the game placing a first serve out wide coupled with a swinging forehand winner into the corner, and a backhand unforced error gave her a commanding 30-0 lead.
It seemed that the opening set was going to be settled by Muguruza, unforced errors returned which allowed the Latvian to break back, and the set was hanging in the balance at 5-5.
Sevastova, formally ranked at 36 took the lead in the match for the first time since leading 2-1, and Muguruza had the task of serving to stay in the first set and attempting to take the first set into a tiebreak.
The French Open champion started the 12th game with authority by coming to the net and placing a forehand smash in the corner, quickly followed by her second ace of the set.
Muguruza's footwork let her down coupled with unforced errors, furthermore gifting Sevastova a set point with a double fault.
The Latvian shocked the Arthur Ashe Stadium crowd, clinching the first set by playing a drop shot which Muguruza failed to retrieve placing it into the net.
The Latvian's momentum continues
Sevastova held her serve in the opening game of the second set, and in the following game, Muguruza's sluggish footwork and unforced errors continued, allowing the former world number 36 to break to love and claim her fourth consecutive game in the process.
A backhand drop shot winner, followed by the Spaniard's backhand going long, helped Sevastova settle into the game. But the game went to deuce, and Muguruza was trying to be aggressive from the baseline. Unfortunately, failing to place a forehand down the line which allowed the Latvian to consolidate the break at 3-0.
Alarm bells were starting to ring for Muguruza as she found herself struggling at 0-30 down in the fourth game but a rushed drive volley tamely into the net following a first serve gave the Latvian more break points for the insurance break.
The Spaniard saved the break point in style with a backhand winner up the line, returning Sevastova's slice drop shot. However, there was more misery for Muguruza as forehand unforced error handed the Latvian the double break that she was in search for.
There was a sense of nervousness in the world number 52's game as she was on the verge of creating a huge upset, and a game filled with tight unforced errors, Muguruza retrieved one of the breaks back but still trailed 4-1.
An exquisite forehand winner down the line from the third seed's racquet came in the third point of the longest rally of the contest at 17 shots but more unforced errors crept in, and another break point chance was handed to Sevastova.
Muguruza attempts to fight back
However, the former world number two found some first serves to sniff out the break point but a mental block seemed to have appeared again for Muguruza with poor footwork allowing Sevastova to regain the double break, and serve for the match at 5-1.
Muguruza continuously tried to be aggressive from the baseline but it wasn't working, helping Sevastova to get to a 30-0 lead to settle down the nerves whilst serving for a huge upset.
The Latvian gained two match points with a forehand down the middle which seemed to be game over for Muguruza, however, Muguruza received a lifeline as Sevastova committed four unforced errors in a row to allow this topsy-turvy encounter to continue at 5-2.
The signs were starting to become ominous for Sevastova as Muguruza was on the comeback trail, portraying her champion's mentality by holding to love, and forced the Latvian to serve for the match again.
In the ninth game, Sevastova hammered down a timely ace down the T but a tight forehand went long, coupled with Muguruza finding a backhand winner in the corner of the court, nonetheless, Sevastova found a good first serve to get the game levelled at 30-30 but more errors handed the Spaniard a third consecutive game to get the match back on serve at 5-4.
Unbelievably, Muguruza had the momentum but three consecutive unforced errors due to feeling tight and poor movement, the Latvian was gifted three more match points but a forehand forced error meant she had two chances to convert, and on the fourth match point, Sevastova upset the Spaniard with a forehand winner to end this contest in 1 hour and 39 minutes.
Match stats
This wasn't a good match in terms of quality as the Latvian had 12 winners and 34 unforced errors, likewise the numbers were poor for Muguruza with 16 winners and 38 unforced errors.
However, the Latvian won 62 per cent of her first serves with Muguruza only gaining 47 per cent.
The world number 52's reward is a third round meeting with 2009 US Open quarterfinalist Kateryna Bondarenko.