MADRID, May 10 (Reuters) - Top seed and world number one Serena Williams was pushed all the way by unseeded Spaniard Anabel Medina Garrigues before triumphing 6-3 0-6 7-5 to make the semi-finals at the Madrid Open on Friday.
The defending champion at the clay event fought back from 4-2 down in the third set to see off the local favourite, who was cheered on by a partisan crowd at the Magic Box Arena.
"It was definitely a battle," Williams told a news conference.
"I obviously didn't do much in the second set, and I think I gave her a lot confidence to play better. I thought she played really well in the third."
Williams made it 26 wins and only one defeat since the start of last year's claycourt season, but was up against an experienced player on the surface.
The 30-year-old Spaniard has the highest number of clay-court title wins with 10 among players currently on the circuit and stunned the American taking the second set to love.
"I wasn't really there," Williams said. "I wasn't really in it. My feet weren't moving. I don't know what happened.
"To turn it around I got up earlier on the changeover and started doing high knees and just stretching and doing anything to try to get my intensity back up where it needed to be.
"I definitely want to cut back on my unforced errors. I had a lot today. Also, I went for a lot more today than I have been doing in my past few matches.
"So I think I'm going to go back to the way I have been playing, and being more calm, and not making as many errors as I did today."
Williams will meet either seventh-seeded Italian Sara Errani or unseeded Russian Ekaterina Makarova in the last four. (Reporting by Mark Elkington, editing by Pritha Sarkar)