America's Serena Williams (right) greets her sister Venus after their Round Four match at the Indian Wells event on Monday. Pic/AFP

Serena Williams admits she has a long way to go to get back to her peak after being knocked out of the Indian Wells event by sister Venus. The younger Williams had progressed to the third round in her first WTA Tour tournament since the 2017 Australian Open, in which she defeated Venus in the final to collect her 23rd Grand Slam title before taking a break to give birth to daughter Alexis Olympia.