ROME, Italy - Garbiñe Muguruza opened a busy day at the Internazionali BNL d'Italia with a hard-fought 6-4, 4-6, 6-2 second-round win over Danielle Collins, triumphing in the all-unseeded affair in two hours and 10 minutes.

In contrast to yesterday's washout, Thursday's packed schedule opened with blue skies, which pleased the two-time semifinalist, who said: "We always want to play with sun - brings good energy." That was certainly the case as she withstood a second-set fightback from Collins to accelerate to victiry.

"Yes, I was just keeping composed," Muguruza said afterwards. "I was playing well. She came up and won the second set. I knew I was on the right path. In the third set I kept doing the same thing and it worked better."

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The first meeting between two 25-year-olds was an intriguing claycourt clash. Although both players center their games around baseline power, red clay has historically been a happy hunting ground for Muguruza, the 2016 Roland Garros champion, while Collins is a relative novice on it: Rome is just the American's eighth tournament on the European terre battue, and she scored only her third career main draw win on it with No.10 seed Caroline Wozniacki's first-round retirement this week.

A month ago in Charleston, though, Collins revealed that she considers green clay to be her favorite surface - and certainly there were few signs of discomfort as she opened the match at a canter. Blitzing winners off her backhand wing at will, the first four games saw the World No.30 pushing an embattled Muguruza to four deuces on the Spaniard's serve, while conceding just one point behind her own delivery.

Read more: Danielle Collins finds her feet on green clay: 'It's one of my favorite surfaces'

But Muguruza's resistance paid off as she extricated herself from those tussles with fine net play and strong serving - and, with her feet now found, powered through three ferocious forehands to break. Though the World No.19's backhand went astray in the next game to hand the advantage back to her opponent, Collins would repay the favor as her forehand broke down - and this time Muguruza would find enough first serves to keep the Australian Open semifinalist at bay, taking her second set point with an emphatic one-two punch.

A pair of mini-marathons set the tone for a second-set turnaround. Collins survived three break points in the opening game before holding with a one-two punch of her own, and the Charleston quarterfinalist proceeded to conjure up a delightful dropshot to take her fourth break point in the subsequent game. By now, both players were vocally fired up: one unreturned Muguruza serve to save a break point elicited a simultaneous "Vamos!" from the Spaniard and a self-castigating "Hit the ball!" from the American.

Two points from a 0-4 deficit, though, the Monterrey champion hit back. A swashbuckling swing volley got her out of trouble and on to the scoreboard, before some dogged counterpunching retrieved the break. As a slew of errors and double faults began to creep into Collins' game, Muguruza reeled off nine out of 10 points to break again for her fourth straight game and a 4-3 lead.

Collins's impact wasn't done, though. A magnificent forehand winner captured the break back - and, rejuvenated, the 2018 Miami semifinalist stormed through the rest of the set as she unleashed her power on every shot, sending down two aces to hold and taking the set as Muguruza committed her fifth double fault of the day.

In light of the narrowly contested first two sets, the decider proved, perhaps surprisingly, to be rather more one-sided. A netted forehand put Collins down an immediate break, and from there Muguruza took control. Brutalizing returns, confident swing volleys and a touch of magic with a pinpoint lob at full stretch stamped the former World No.1's authority on the set: Muguruza would lose just four points en route to a 5-0 lead, at one point reeling off 13 in a row.

Closing the match out would be less straightforward. The two-time major champion squandered a match point for a bagel set as she netted a mid-court backhand, and Collins seized the lifeline to claw two games back. But Muguruza made no mistake stepping up to the line a second time, delivering an immaculate hold to serve out the win to love, finishing with an exclamation mark as she hammered down a fourth ace of the day.

Next up for the 2016 and 2017 semifinalist here is a clash later today with another former World No.1, Victoria Azarenka, with a quarterfinal berth at stake.