Australian Open -- Linda Noskova's upset of No. 1 Iga Swiatek - ESPN

MELBOURNE, Australia — World No. 1 Iga Swiatek has been upset in the third round of the Australian Open by 50th-ranked Czech teen Linda Noskova.

Swiatek claimed the first set and looked likely to secure passage into the fourth round, but Noskova, 19, rallied with steely resolve to save break points and then convert her own to take the second.

With the pressure on the world No. 1 Swiatek — who had won 67 of her previous 68 matches against players ranked outside the top 50 — Noskova broke twice in the decider to secure her place in the second week.

Swiatek's loss means it's just the second time the No. 1-seeded woman hasn't made it to the fourth round of the Australian Open, after Virginia Ruzici was dumped in the round of 32 in 1979. Noskova is the first teenager to defeat a WTA No. 1 in a major since 19-year-old Petra Kvitova defeated Dinara Safina in the third round of the 2009 US Open.

So what went wrong for Swiatek? Here are three takeaways from her early exit.

In a tight second set, the four-time major champ twice had the opportunity to break her younger opponent's serve but failed to take advantage.

With Noskova serving in the fifth game at 2-2, Swiatek was unable to convert a break point after her opponent sent down a serve wide to the backhand that Swiatek couldn't get back over the net.

In Noskova's next service game, Swiatek again had a break-point opportunity, and on her opponent's second serve, but she hit the backhand into the net. Swiatek then got broken to love, as Noskova reeled off 11 of the next 12 points to take the set.

«I felt like I had everything under control until she broke me in the second set,» Swiatek said.

«I had couple of chances to break her in second set and I didn't use them. So that's a