Miami - Top-ranked defending champion Novak Djokovic withstood back spasms throughout the second set on Wednesday to defeat Tomas Berdych 6-3, 6-3 and reach the ATP and WTA Miami Open semi-finals.
Djokovic, trying to match Andre Agassi's record of six Miami titles with his third in a row, will play Belgian 15th seed David Goffin on Friday for a berth in Sunday's final.
The 28-year-old Serbian won his 14th consecutive match at the hard-court event and his 28th out of 29, but needed a gritty performance after back pain began early in the second set, prompting him to have massage therapy before serving in the sixth game.
"Due to windy conditions on the court, it was hard to find a good rhythm to serve," Djokovic said. "I had a little bit of a spasm in the back but (the trainer) did a great job and I was able to finish the match."
Asked if he had any worries the spasms might become a long-term issue, Djokovic said: "No concerns. None at all."
On the women's side, reigning Australian Open champion Angelique Kerber, the second seed from Germany, and two-time Australian Open champion Victoria Azarenka of Belarus advanced to a Thursday semi-final showdown.
Both have finals wins over top-ranked Serena Williams this year, Kerber at the Australian Open and Azarenka at Indian Wells.
Berdych lost his 10th consecutive match to Djokovic, whose domination of their career rivalry reached 23-2. Berdych's last victory over Djokovic was in a 2013 Rome quarter-final.
"If you have that many head-to-head, it can help, but not substantially," Djokovic said.
Djokovic blasted a crosscourt forehand winner to break Berdych for a 3-1 lead and held from there to claim the first set, in which the Czech had 21 unforced errors.
Berdych surrendered a break to open the second set but Djokovic first reached for his lower back in the next game but held and broke again to end the match.
"Overall, this is the best match I've played in the tournament," Djokovic said. "I feel better than I did last year at the same stage. I'm hoping I can keep the same trajectory."
Djokovic won his 11th Grand Slam title two months ago at the Australian Open and also has crowns this year at Indian Wells and Doha.
Goffin matched his semi-final run from Indian Wells by downing French 18th seed Gilles Simon 3-6, 6-2, 6-1.
"Feeling great," Goffin said. "Confident for the rest of the week and the season."
But he is 0-3 against Djokovic, losing in the 2013 French Open first round and at Cincinnati in 2013 and 2015.
"He's going to be very dangerous but I like my chances," Djokovic said.
Former world number one Azarenka defeated British 24th seed Johanna Konta 6-4, 6-2 while Kerber cruised into the semi-finals, downing US 22nd seed Madison Keys 6-3, 6-2.
The German second seed, the last of the top 12 remaining, is 1-6 lifetime against Azarenka, but won their most recent meeting in the Australian Open quarter-finals on the way to the title.
"We have played some really tough matches," Kerber said. "I know I have to play my best tennis against her. I will be ready."Eighth-ranked Azarenka, who won the 2009 and 2011 Miami titles, will jump to fifth in the world next week.
Azarenka could become only the third woman to win back-to-back in Miami humidity and Indian Wells desert heat after Steffi Graf in 1994 and 1996 and Kim Clijsters in 2005.
"If I win, that's great," Azarenka said. "But right now I'm looking to the semis."
Two-time Grand Slam champion Svetlana Kuznetsova meets Swiss 19th seed Timea Bacsinszky in the other semi-final. The 30-year-old Russian has won both their previous meetings.Scores on Wednesday from the ninth day of the ATP and WTA Miami Open (x denotes seeded player):
David Goffin (BEL x15) bt Gilles Simon (FRA x18) 3-6, 6-2, 6-1
Novak Djokovic (SRB x1) bt Tomas Berdych (CZE x7) 6-3, 6-3
Victoria Azarenka (BLR x13) bt Johanna Konta (GBR x24) 6-4, 6-2
Angelique Kerber (GER x2) bt Madison Keys (USA x22) 6-3, 6-2