Carlos Alcaraz's bid for a Sunshine Double crumbled in dramatic fashion as the top-seeded Spaniard fell 6-2, 6-4 to Grigor Dimitrov on Thursday.

Dimitrov, the Bulgarian 11th seed, dominated the match, winning 77% of his first-serve points compared to Alcaraz's 56%.

He also saved four out of five break points and broke Alcaraz's serve four times during the 92-minute clash.

The defeat was particularly tough for Alcaraz, who came to Miami brimming with confidence after winning the Indian Wells title just 11 days prior.

Despite his impressive form, Alcaraz fell short of making history as the first man since Roger Federer in 2017 to achieve the elusive Sunshine Double.

"Overall, to win against him, you have to play at your best. That's just how it is," Dimitrov said after his second victory over world number two Alcaraz in as many meetings.

"I came into the match focused, and I think it was extremely clear what I had to do.

"Sometimes simplicity is genius. It's very hard to do it, especially when you play against an opponent like that, but I was able to dictate the game, read the game a bit better than the last time.

"Overall, a very great match on my end, and I'm just happy I finished in straight sets."

Up next for Dimitrov will be German fourth seed Zverev, who overcame tricky conditions to beat Hungary's Fabian Marozsan 6-3, 7-5 in the day's first match on the Stadium court.

"We have limited time to celebrate, to get ready to prepare. Right now the most important thing is to prepare for the match," added the 12th-ranked Dimitrov, who can climb into the top 10 with a victory.

"Very grateful to be that far into a Masters event, and I'm very excited for what's next."

Zverev attacked Marozsan's serve and converted three of his seven break-point chances, swatted aside the two break points he faced, and won 80% of his first-serve points en route to the last four in Miami, where he has yet to drop a set.

Despite not dropping a set in windy conditions, Zverev had his hands full with Marozsan, who is making his Miami debut and enjoyed top-10 upsets over Holger Rune and Alex de Minaur on the way to the quarter-finals.

"If he continues playing like that, he's going to rise up the rankings very quickly, and he's going to be one of those (top 10) guys himself," Zverev said in his on-court interview.

"When we are in control, I think all top players, when they are in control they feel like they can manage the match, manipulate the match a little bit in their favor.

"But against him, that's not possible. That's why he has such a great top-10 record, and he's an unbelievable player."

Zverev's win, sealed with a break when he unleashed a brilliant backhand down the line, marked his return to the Miami Open semi-finals for the first time since his runner-up finish in 2018.