NEW YORK -- How do you summon the strength and the motivation to replicate a lifetime achievement -- almost immediately after the momentous fact?

That was the awesome challenge facing No.7 seed Zheng Qinwen and No.8 Barbora Krejcikova on Wednesday at the US Open when they played back-to-back second-round matches on the Grandstand court.

Zheng, who won the Olympic singles gold medal in Paris earlier this month, was forced into comeback mode for the second straight match but rallied to defeat Erika Andreeva 6-7 (3), 6-1, 6-2. Zheng has now won 14 of her past 15 matches.

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Meanwhile, Krejcikova -- crowned the Wimbledon champion last month -- fell to qualifier Elena-Gabriela Ruse 6-4, 7-5.

It was the first major loss for Krejcikova after compiling a streak of eight straight -- and the upset of the tournament so far. Ruse, a 26-year-old from Romania, is ranked No.122 among Hologic WTA Tour players. Krejcikova, one of the WTA Tour’s most consistent players, had won 15 of past 16 matches against players ranked outside the Top 100. 

Ruse reached the third round of a Grand Slam for the first time in her career, scoring only her second Top 10 win.

The surprising loss by Krejcikova underlined just how difficult it is to reset after a career-defining victory.

And for Zheng, when dropped the first set of her opening match against Amanda Anisimova, her thoughts flashed back to a less-than-inspiring spring. After reaching the Australian Open final, she went 5-6 over her next six tournaments.

“It’s the typical match I will lose, especially after huge success,” Zheng told reporters later. “Because as I know myself, usually after huge success I will get a little bit too high -- and until the reality slap me down again.”

Zheng rallied to beat Anisimova 4-6, 6-4 6-2.

“So this time when I get a success,” she added, “I’m telling myself, `I don’t want to let this happen. I’m going to continue working hard, keep the stable mindset.’ To win this match means I make one step forward in my mental side.”

Wednesday’s victory was more of a leap. Zheng looked sluggish in the first set, seeing her serve broken twice and landing only one first serve in the tiebreak. In the second set, she cracked seven aces alone and won all 13 of her first-serve points.

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In the opening game of the third set, Andreeva saved six break points -- but not the seventh. Zheng forced an errant backhand and took immediate control.

Zheng finished with an eye-popping 20 aces (and a slew of balls off the frame), giving her 32 in two matches. It was the fifth time this year Zheng served up double-digit aces -- the most among WTA Tour players.

“You have the first [gold medal], of course you’re going to stay long time in the successful feeling,” Zheng said. “I done that in Australian Open, but I was just in the final, and the effect takes me so long to come back to reality.

“I had this experience already, so this time when I had success in Olympic Games, to come to next tournament, I say, `Everything starts zero. You are not anymore Olympic champion. Just be humble and trying to work, fight every single match, because if you don't fight, you have a big chance you lost.’”

The swirl of obligations following Wimbledon, Krejcikova said, far surpassed those after her major breakthrough three years ago at Roland Garros. There was a flood of appearances and interviews back home.

“I enjoyed it, but on the other hand it took a lot of energy from me,” Krejcikova said. “I mean, I’m still trying to figure out how to get everything together and how to just find a good balance.”

Maintaining that balance was difficult, as evidenced in her 7-6 (3), 6-2 victory over qualifier Marina Bassols Ribera first-round win. Against Ruse, it proved impossible.

In fairness, Ruse played a spectacular match, feasting on Krejcikova’s second serve, winning 20 of those 32 points. She was also more aggressive, stroking 28 winners and making only 15 unforced errors. Krejcikova’s numbers were 27 and 24, respectively. Ruse finished with eight aces, while Krejcikova stroked seven double faults.

Ruse broke Krejcikova’s serve in the sixth and 10th games of the first set and took the frame on her third set point when Krejcikova’s backhand soared wide. Krejcikova forged a 5-3 lead in the second set, but Ruse rallied to win the last four games. 

When it was over, Ruse fell to the ground and covered her mouth with her hands as if she couldn’t believe the result.

The 28-year-old from the Czech Republic has weathered a stormy season that included a back injury, a lingering illness, a winless clay season and a PIF WTA Ranking that dipped into the 30s.

“Before Wimbledon I had many doubts and things just weren’t going my way,” Krejcikova told reporters before the tournament. “After Wimbledon, I told myself just please never doubt yourself again, because there is no reason to do that.”