OPEN NOTES

Meanwhile, Porzingis, who is nursing a bruised knee, is in Latvia gearing up for the start Friday of the European Championships.

After Ostapenko became the first Latvian to win a major, Porzingis tweeted his congratulations on her “historic’’ victory in Paris.

“I’m actually not on Twitter so I didn’t know that,’’ she said. “I knew that he followed me on Instragram, so that’s really cool. It’s great that he posted I won the French Open.’’

Madison Keys hit the right notes and the right shots in the right moments in defeating Belgium’s Elise

Mertens 6-3, 7-6 (6) in her first-round match early Tuesday night at Ashe.

The 22-year-old Keys, coming off an encouraging summer after missing the season’s first two months following left wrist surgery, prevailed after being broken at 6-5 in the second set.

The second-highest seeded American woman (15th) behind Venus Williams (ninth), Keys — aggressive throughout — held off a set point at 5-6 in the tiebreak before taking the final three points to advance. Keys will face the winner of Wednesday’s match between Germany’s Tatjana Maria and American wild-card entry Ashley Kratzer. No. 1 Karolina Pliskova, last year’s runner-up, cruised through the opening match on Ashe, 6-2, 6-1 over Magda Linette. The draw’s most dangerous server (non- Maria Sharapova division), Pliskova recorded eight aces.