ROME, Italy - A tightly-fought first-round battle of power at the Internazionali BNL d'Italia saw the unseeded Amanda Anisimova edge No.16 seed Donna Vekic 7-6(4), 7-6(6) in two hours and 27 minutes after twice coming from a break down in the first set and then saving triple set point in the second.

It was an intriguing first encounter between two players just one spot away from each other in the rankings - though Vekic was the seed here, the post-US Open movements had meant that she was the lower-ranked of the two, World No.28 to Anisimova's World No.27. The contest bore out this parity: despite 10 breaks of serve in total, neither player was able to pull away from the other for more than a two-game advantage at any point, and the result remained on a knife-edge to the end, with a missed putaway from each at the end of the second set providing real 'sliding doors' moments.

Ultimately, it was the American's superior serving, aggression and capacity to rebound from disappointment that was crucial: Anisimova landed 70% of her first serves compared to Vekic's 49%, found 39 winners to Vekic's 23 and found some impressive mental strength to save a second set that had all but slipped from her grasp.

The teenager had to overcome a slow start, dropping serve in the opening game thanks to four straight unforced errors. But after battling through five deuces and staving off two points to fall behind a double break, Anisimova began to get her teeth into the match and slowly but surely forced her way back in.

The ensuing five-game sequence would find Anisimova posting rapid-fire holds while piling the pressure on her opponent. Vekic, who landed just 41% of her first serves in the first set, sent down one double fault in each of her first four service games and committed 17 unforced errors across the opening act, was forced to save break points in the fourth and sixth games as Anisimova teed off every time she received a second serve.

Though a combination of luck - a dead net cord - and skill - a neat forehand volley - staved off these dangers, the trajectory of the match had swung towards the Roland Garros semifinalist, who found her breakthrough in the eighth game courtesy of a Vekic double fault.

Anisimova would nearly squander her fightback, leaking a slew of unforced errors to drop serve again - but Vekic, serving for the set, repaid her in kind. Heading into the ensuing tiebreak - having won the point of the match with a scrambling, well-anticipated backhand pass en route - Anisimova took control, leaping out to a 4-0 lead with her third ace, staving off a Vekic fightback with a brilliantly finessed reflex volley and sealing the set as the Croat netted a forehand.

A surging Anisimova pressed home her advantage as the second set got under way, playing her most confident tennis of the match - as evidenced by a pair of rare but perfectly played dropshots to aid her in moving into a 2-0 lead. But at this point, the 2019 Bogota champion wobbled. Three double faults across her next two service games, accompanied by a slew of unforced errors as Vekic posted a pair of unusually straightforward holds, meant that it was the Croat's turn to take back momentum with four games in a row.

Though there were passages of play where Anisimova's looseness with her groundstrokes would prove a significant hurdle - the 19-year-old tallied 43 unforced errors today - she was also able to come up with the most remarkable shotmaking when she needed to, including a greater variety than her opponent in her repertoire. A pair of sizzling defensive forehands on the run stemmed the scoreboard flow and garnered her the break back; a single-handed defensive backhand slice was key to successfully serving to stay in the set.

At 5-5, though, Anisimova went back to her roots. Vekic's first serve percentage had improved, but not enough: the Auckland semifinalist unleashed a pair of ferocious forehand return winners to break for 6-5. Here, though, matters took a turn for the complicated.

Having made her way to match point thanks to a fourth ace, Anisimova merely had to put away a smash, with Vekic haring in the wrong direction, to wrap up victory. But, looking into the sun, the youngster netted it - and a few points later found herself embroiled in another tiebreak, one that she added another twist to with a medical timeout two points in to take care of a finger injury.

On resumption, it was Vekic who initially seemed to have best sustained her equilibrium, coming up with a textbook one-two punch to reach triple set point at 6-3. But with Anisimova desperately scrambling, the first saw the 24-year-old take her turn at making a hash out of a putaway, sending a forehand flying out of court. Now, it was Anisimova who had been granted a lifeline, and she made the most of it.

A dropshot so perfectly executed that it made no difference that Vekic had anticipated it saved the second set point, before consecutive forehand winners brought Anisimova to her second match point - sealed with a netted forehand from her opponent. A relieved Anisimova will now face another barrage of power in the second round, in the form of either Dayana Yastremska or wildcard Camila Giorgi.

2020 Rome highlights: Anisimova squeezes past Vekic