Mariano Navone delivered one of the biggest upsets in recent Grand Slam history on the opening day of the 2026 US Open, defeating fourth seed Novak Djokovic in a gruelling five-set contest at Arthur Ashe Stadium in New York on Monday. The result hands Djokovic his first first-round loss at a Grand Slam since 2006 — a span of two decades.

Navone, the Argentine qualifier, prevailed 7-6(5), 5-7, 4-6, 6-2, 6-1 in a match that stretched four hours and 36 minutes, making it the longest opening-round match in Grand Slam history. The 24-time Grand Slam champion appeared to fade physically in the closing stages, with the closed roof at Arthur Ashe Stadium doing little to ease conditions for the Serb.

Djokovic's Physical Struggles

Djokovic, a four-time US Open champion, began the match with intent but visibly ran out of steam as the contest wore on. The physical difficulties that had disrupted his campaign at Cincinnati in the lead-up to the Slam resurfaced, with winners drying up and errors mounting in the decisive fourth and fifth sets. Navone, by contrast, grew stronger as the match progressed, pulling away decisively in the final two sets.

Notably, Djokovic had never before lost in the first round of a Grand Slam since a shock exit at the 2006 edition of a major — a run of near-flawless Grand Slam entries spanning two decades. This defeat marks a significant moment in the twilight of his career.

Medvedev Makes a Composed Return

The other headline from opening day was the controlled return of 2021 US Open champion Daniil Medvedev. After suffering a chaotic first-round exit to Benjamin Bonzi at the 2025 edition — a match that did not conclude until 12:49 a.m. local time — Medvedev was determined to set a different tone this year.

The former World No. 1 dispatched qualifier Hugo Gaston 6-4, 6-2, 6-4 in two hours and 14 minutes, advancing to the second round for the eighth time in his US Open career. The win lifted him two spots to No. 6 in the ATP Live Rankings. Defending just 10 points this fortnight, Medvedev has a significant opportunity to climb deeper into the world's Top 10.

He will next face either American wild card Sebastian Gorzny or Raphael Collignon in the second round.

Other First-Round Highlights

American hope Tommy Paul recovered from a sluggish opening set to defeat qualifier Coleman Wong 6-7(3), 6-1, 6-3, 6-3. Paul is chasing a quarter-final berth at the US Open for the first time — a result that would complete a set of quarter-final appearances at all four Grand Slam tournaments, making him the only active American man to achieve that distinction.

Croatian youngster Dino Prizmic, 21, produced a stunning comeback, saving both match points at 4-5 in the fifth set before reeling off three straight games to win. It was Prizmic's first US Open main-draw victory. Fellow Next Gen ATP Finals alumni Luca Van Assche also impressed, upsetting 29th seed Cameron Norrie of Britain 6-7(8), 6-2, 6-2, 6-3, advancing to face Denis Shapovalov in the second round.

What to Watch Next

With Djokovic out, the men's draw at Flushing Meadows has opened up considerably. Medvedev, buoyed by a clean opening win, will be among the favourites to capitalise. The second round begins with several intriguing matchups, and all eyes will be on whether the next generation — Navone, Prizmic, Van Assche — can sustain their early momentum deep into the fortnight.