World No. 1 Simona Halep crashed out of the US Open first round for the second consecutive year, losing to 44th-ranked Estonian Kaia Kanepi 6-2, 6-4 on the new Louis Armstrong stadium on Monday.

Halep entered the tournament as the favourite having won Montreal, and reached the final of Cincinnati, in the build-up.

Kanepi is a former world No. 15 and a two-time US Open quarter-finalist (2010, 2017).

Here are the numbers surrounding her stunning upset.

1 — Halep is the first US Open women’s top seed in the Open Era to lose in the first round, and the sixth Grand Slam women’s No. 1 seed to exit at that stage.

1 — Kanepi is the first and only Estonian to defeat a reigning world No. 1. She did it for the first time against Caroline Wozniacki in Tokyo 2011.

7/9 — Kanepi was successful in seven of the nine net points she played. Her aggressiveness that allowed her to go up front paid off 78 per cent of the time.

9 — Halep committed just nine unforced errors in her defeat to Kanepi, who was clearly forcing the error from her top-seeded opponent.

12 — times Halep has lost in a Grand Slam first round, from 34 main draw appearances.

26 — winners off the Kanepi racquet against Halep, against 28 unforced errors.

39 — months since Kanepi had last defeated a top-20 player (since Madrid 2015).

46 — Halep entered the US Open as the match-wins leader on tour this season (46-8) and hard-court match-wins leader (28-4).

51% — Kanepi won 51 per cent of her receiving points, 41 per cent on Halep’s first serve, and an impressive 70 per cent on the Romanian’s second serve.

56% — Kanepi did well keeping the rallies short against Halep. A total of 56 per cent of the points (60/107) were rallies of 0-4 shots. The Estonian won 58 per cent of such points. The average rally length was 4.46 shots.