"For sure, I'm still trying to improve my tennis", said the 2016 year-end World No.1.
Needing to move to the semifinals to have a chance of staying in the Top 5, Pliskova will face Pliskova's victory sets up a quarterfinal encounter for the World No.5 against Naomi Osaka who defeated 6-1 5-7 6-1 Maria Sakkari.
Williams, a 23-time Grand Slam champion and the most successful player of the Open era, was knocked out by her sister Venus in round three in California.
Halep breezed through her fourth round match with a 7-5, 6-1 win over China's Wang Qiang and eighth seed Venus Williams faced a stern test from Anastasija Sevastova but held on for a 7-6 (8/6), 6-4 victory.
First she will have to get past unseeded Croatian Martic, who advanced to the last eight with a 6-3 7-6 (7-4) win over Marketa Vondrousova.
Halep needs to reach the final at the Tennis Garden to hang onto her top WTA ranking against a charge from Australian Open victor and formerly top-ranked Caroline Wozniacki.
"I wasn't missing that much", she said.
Pakistani diplomats, families in New Delhi reportedly being harassed
The port is crucial for India as it plans on creating a trade and transport corridor to Afghanistan while bypassing Pakistan. After years of trying to make the Iran-Pakistan-India gas pipeline a reality, Iran and India had given up on Pakistan.
Halep won this event in 2015 and Wozniacki won it in 2011.
Only Wozniacki can usurp her atop the WTA rankings after Indian Wells, but she must win the title and hope Halep lose before the final.
Williams, who has yet to drop a set, will face either Carla Suarez Navarro or Danielle Collins in the last eight.
Simona Halep is into the quarterfinals at Indian Wells.
Halep called for a timeout in the first set so her coach Darren Cahill could come down to the court to discuss strategy.
Former world number one Karolina Pliskova used her powerful serve to overwhelm 16-year-old Amanda Anisimova and reach the quarter-finals for the third year in a row. Kerber was undeterred, and broke the Garcia serve another time, on her fifth break point in a nine-minute game after another strong forehand forced an error from Garcia. She is on the verge of her second career singles title at Indian Wells.
She used her protected ranking to play at Wimbledon in the same year.