American youngster continues to impress

The top-ranked American in the U.S. Open has been bounced out of Flushing Meadows, while the unknown teenage qualifier is on to the third round.

No. 19 Steve Johnson had the misfortune of Argentine Juan Martin del Potro finding his lost form at his expense, falling 7-6 (5), 6-3, 6-2 at Arthur Ashe Stadium. But Jared Donaldson’s dream run continued with a mature-looking 7-5, 6-3, 6-3 win over 32nd-seeded veteran Viktor Troicki.

At 19, Donaldson is the youngest American into the third round here since Donald Young in 2007.

“When the big point’s coming, it’s important to play within yourself, play what you know works,’’ Donaldson said. “I just try to play the big points well.”

Instead of the usually academy or USTA Player Development, Donaldson cut his teeth training for two years on the red clay down in Argentina. He developed more than just a love of Boca Juniors; better movement and discipline. And even though he’s flown under the radar, that could be changing.

“The other guys deserve a lot more attention than myself. Honestly, whether or not I get a lot of attention, I’m still 120 in the world. That’s not amazing, not where I want to end up,’’ Donaldson said.

Johnson got blitzed by del Potro, who hit 15 aces and 33 winners, hearing chants of Olé, Olé, Olé against an American foe.

“I like when I heard these songs to me. It’s like a soccer stadium. ... It’s amazing for me having this love,’’ del Potro said.

“It’s tough [if you don’t] play your best tennis against a guy as good as Juan,’’ Johnson said of del Potro, who won the 2009 U.S. Open title before undergoing three wrist surgeries. But when ranked No. 141 this summer, he upset No. 1 Novak Djokovic and No. 5 Rafael Nadal en route to the Rio Olympic final.