Iga Swiatek progressed to her fourth WTA 1000 semi-final on Wednesday at the Miami Open, defeating Petra Kvitova 6-3 6-3.

After taking out tournaments in Doha and Indian Wells this year, the 20-year-old's undefeated streak now moves to 15 in a row.

Kvitova largely stayed in points in the opening exchanges and held a higher first-serve rate than Swiatek, but indicative of the form the Polish star is currently in, she played with clarity and did not hesitate when opportunities presented.

Along with winning six of eight points on Kvitova's second serve in the first set, the soon-to-be world number one converted on her sole chance at break point, claiming the crucial break in the sixth game before closing the opening set out.

After a tough service hold in the fourth game and four initial chances at break point in the second set, Swiatek made it count on her fifth attempt, spectacularly managing to move the 28th seed around the court and turn defence into attack.

Seeing the finish line, the Polish second seed grew increasingly assertive in both serve and shot selection to both secure the break and see out the match, even claiming a second break for a punctuation mark.

Swiatek will face Jessica Pegula, who is also through to the semi-finals after Paula Badosa retired from their matchup due to a viral illness.

Pegula was leading 4-1 after only 18 minutes of play when Badosa retired, having won four straight games after initially dropping her serve.

The 28-year-old has now won her last two matches in Miami via retirement after she advanced past Anhelina Kalinina in the fourth round, winning the first set 6-0.

If Pegula defeats Swiatek in the semi-final, it would make for her maiden WTA 1000 final appearance.