MIAMI, FL, USA - No.6 seed Jelena Ostapenko's commitment to dramatic, unpredictable shotmaking was on full display as she eked out a tight 7-6(3), 7-6(5) win over No.4 seed Elina Svitolina in the quarterfinals of the Miami Open, successfully walking a thrilling tightrope of 44 winners to 42 unforced errors.

"Before the match I knew that I have to be very aggressive," Ostapenko stated afterwards. "And when I had a chance, I was going for it. Of course I was missing some because I was trying to play aggressive the whole match, but I think my winners are more than the unforced errors."

The win marks the Roland Garros champion's first semifinal showing of 2018, and the first time she has won four consecutive matches since her Seoul title run last September. Svitolina, meanwhile, has still just one semifinal to her name at Premier Mandatory level or above - Beijing in 2016.

Ostapenko made a dream start to the match, breaking her higher-ranked opponent to love; and though four unforced errors in the next game repaid the favor, her ultra-aggressive intent on return would set the tone for the match.

At every opportunity, the Latvian would seek to dictate from the first stroke on the Svitolina serve - stepping in to take full cuts at the Ukrainian's second delivery, but also showing little mercy whenever a first serve landed in her striking zone and pinning her opponent firmly behind the baseline.

Few who have watched Ostapenko's fearless ballstriking over the past year will have come away thinking the 20-year-old's problem is too little aggression - but, she says, this is precisely what she has been working on.

"I think maybe the other tournaments I was trying to, like, play more balls in the court and without any aggressivity," she revealed. "But now I think I really go for the shot when I need to and I'm not afraid to risk."

The strategy paid off with three breaks of serve across the first set, with Ostapenko asserting that baseline dominance via stunning down-the-line winners and sharply angled shots that, barely skimming the net, not even Svitolina's scurrying could track down. Towards the end of the set, she would even feel confident enough to follow some groundstroke hammer blows with the most delicate of dropshots.

The flipside, though, was the 20-year-old's inability to use her own serve as a platform for similarly brilliant shotmaking. Though Ostapenko played one flawless service game - consisting of a drive volley winner, a backhand winner down the line, an ace and an incredible scooped get crosscourt - to hold for 3-1, too often rallies behind her delivery would end in error.

Three times Svitolina would peg Ostapenko's lead back, including when the Roland Garros champion offered up her wildest four unforced errors as she attempted to serve the set out. But when it came down to the most crucial points of all, it was the younger player who proved better able to control her game. Two points from losing the set at 5-6, Ostapenko clattered a pair of winners past her rival - and then righted the ship in the tiebreak, taking the first two points and the final five with impeccable power hitting to seal a topsy-turvy opener.

"I was hurting a little bit today, but it was on and off all the time," revealed Svitolina afterwards. "Mentally I was a little bit on and off, as well, and didn't really focus on the right moments and the right things, and, you know, the small things, because she's such a great player. She doesn't miss those opportunities."

Such is Ostapenko's commitment to first-strike tennis that opponents can struggle to assert their own games. Svitolina, though, champion already in Brisbane and Dubai in 2018, had begun to probe her options while trying to get back into the first set: breaking up the rallies with slice, for instance, had invariably drawn an Ostapenko error.

The 23-year-old continued to do so at the start of the second set, as well as striking out with her own groundstrokes. Having notched up just four winners over the first set, Svitolina had already exceeded that number by the sixth game of the next.

Afterwards, the 11-time WTA Tour champion emphasized that she is happy with how her game is progressing. "I'm changing a little bit my game now and playing more aggressive," she said. "Just improving in general. That's tennis, you know. This is progress, you know. We have so many weeks on tour. That's why you cannot escape [from] losing the matches - and from those kind of matches we learn and move forward."

A clean return winner ensured an immediate break of serve for the Australian Open quarterfinalist, as well as giving Ostapenko a taste of her own medicine - and now, it was the newly minted member of the Top 5 playing catch-up.

In a reversal of the first set, Svitolina would go up a break three times - but in contrast to how she had played with a lead in the opener, Ostapenko was able to summon some of her most accurate hitting when behind while maintaining her aggression.

Once more, the set would be decided by a tiebreak - and once more, Ostapenko's knack for raising her game on big points would come to the fore. On the second point, Svitolina brought out an array of slices and spins - but this time, Ostapenko was patient in surviving the rally until an opportunity came for the winner.

Accelerating to a 6-2 lead, it would take four match points for the World No.5 to get over the line - but despite having blown two with wild, overly aggressive errors, there was no backing down. A scorching crosscourt backhand winner, Ostapenko's 44th of the day, sealed a spot in her first Miami semifinal against either No.8 seed Venus Williams or qualifier Danielle Collins.

"I think I was just rushing a little bit too much," said Ostapenko of her mini-drama at the end of the match. "I wanted to hit winner from almost every position. I think that I had to play a little bit smarter - but in general, I think that I was aggressive today helped me."