Serena Williams will renew her era-defining rivalry with elder sister Venus Williams when the pair face off for the 29th time at the Indian Wells Masters on Monday.
Serena is competing in her first event on the WTA Tour since overcoming Venus in the 2017 Australian Open final, when she made history and took a 17-11 lead in their head-to-head record.
The Williams sisters enjoyed a prolonged period at the peak of the women's game following the turn of the millennium, accumulating an astonishing 30 grand slam singles titles between them and combining for major doubles glory on 14 occasions.
Ahead of their meeting in their home state of California, we look back at some of their key meetings over the year.
Venus d. Serena 6-1 4-6 6-4 – Miami Open final, 1999
The sisters' first two encounters saw Venus triumph at the Australian Open and Rome Masters, the latter at the quarter-final stage, and she kept up her 100 per cent record in their first final meeting.
Defending champion Venus overcame Serena, at the time aged just 17, but it was the younger sibling that claimed the first grand slam title at the US Open later that year.
Venus d. Serena 6-2 6-4 – US Open final, 2001
Venus beat Serena in straight sets en route to claiming the 2000 Wimbledon title, the first major of her career, and their maiden meeting in a grand slam final ended in the same manner.
It took Venus just 69 minutes to wrap up the victory, taking a 5-2 lead over her sister in their head-to-head record.
Serena d. Venus 7-6 (7-4) 3-6 6-4 – Australian Open final, 2003
The last three majors of 2002 produced all-Williams finals, Serena winning on every occasion.
An astonishing fourth in succession came at Melbourne Park, and once more it was the younger sibling who emerged triumphant to hold all major titles simultaneously in the most tightly contested encounter of their still burgeoning careers.
It was Serena's fifth grand slam and moved her ahead of Venus, and was made all the sweeter by a semi-final triumph over Kim Clijsters that saw her save two match points and fight from 5-1 down in the third set to win.
Venus d. Serena 7-5 6-4 – Wimbledon final, 2008
Serena also beat Venus in the 2003 Wimbledon final, and it would be another five years until they battled it out for another grand slam.
Venus had struggled with a persistent wrist injury in the intervening period, while Serena battled a series of physical and mental issues.
Their return to the grandest stage saw Venus win a fifth Wimbledon title, which she is still yet to add to.
Venus d Serena 6-7 (2-7) 6-2 6-3 – Rogers Cup semi-final, 2014
By this point Serena had comfortably established herself as the dominant force in women's tennis, sitting at the top of the rankings for a period of 186 consecutive weeks between 2013 and 2016.
However, she suffered her first defeat to an unseeded Venus since 2009 in Montreal, with a pair of costly errors in the third set seeing her give away an advantage she was unable to claw back.
Serena d. Venus 6-4 6-4 – Australian Open final, 2017
Venus was enjoying a renaissance late in her career when, aged 36, she progressed to a ninth major final meeting with her younger sister.
Victory never looked in doubt for Serena, who won in straight sets to set an Open-era record of 23 grand slam titles – surpassing Steffi Graf – and return to world number one.
The triumph was made all the more remarkable by the fact she was in the early stages of pregnancy with her first child, meaning it proved to be her last match on the WTA Tour for over a year.