MELBOURNE, Australia (AP) Asked what the future might hold for her young opponent, Venus Williams offered some heartfelt advice that could easily apply to her own career.

''Sky's the limit,'' said the 34-year-old Williams. ''There is no limit on what you can achieve. No one can stop you.''

''Sometimes you may not win every match, but there's a lot of them you can win,'' said the seven-time Grand Slam champion. ''Really, the sky's the limit for her and anyone out there.''

Williams did not win her quarterfinal Wednesday at the Australian Open. That honor went to 19-year-old Madison Keys, a composed and confident power hitter who might be the future of American women's tennis. After beating Williams 6-3, 4-6, 6-4, Keys now faces her first Grand Slam semifinal against Venus's celebrated sister, Serena, who has already won 18 major titles.

But for 10 days, Venus' impressive run at the Australian Open provided one of the tournament's feel-good story lines. It was the first time since 2010, that Williams, who has suffered from an auto-immune illness, had reached a Grand Slam quarterfinal.

Some called it a comeback, or a late-career resurgence. It was a topic of conversation among other players who called her an inspiration, and in the tennis community at-large.

''How great is it to see her back playing great tennis deep into a major,'' now-retired American player, Andy Roddick, tweeted Wednesday. ''The sport is better for it.''

Tennis great Billie Jean King had been sending tweets of encouragement throughout the tournament, including one saying, ''I am inspired by (at)Venuswilliams every time she takes the court.''

For the first time in years, Williams did not face a single question in her post-match news conferences about retirement, so she did not have to reiterate that she plans to keep playing as long as she still enjoys it. She talked instead about how she still loves to win - and at this stage she wants to win big.

''For me I like to win titles, whether it's a smaller event or a big event,'' she said. ''That's what I play for.''

In her two decades on the tour, Williams has won 46 titles, including her most recent one earlier this year in Auckland.

She joked about her age, and Serena's who is 33 and showing no sign of slowing down.

''We just can't figure out how we're still here,'' Venus said. ''I think our perspective is we're still quite good at what we do. While we're here, we're going to be here.''

At times during her stay in Melbourne, she talked about how she was in a good place both mentally and physically on the court, how her years of experience now help her tactics in matches, how she has learned to manage her illness, an auto-immune condition called Sjogren's syndrome, with a diet to reduce inflammation, exercise and knowing her body's limits.

In 2011, she announced she was suffering from the condition, which can cause joint pain and sap energy, and took seven months off from tennis. After tumbling in the rankings to outside the top 100, she climbed back to No. 24 by the end of 2012.

She is now No. 18 and as a result of reaching the quarterfinals in Melbourne is projected to move up to No. 11 when the new rankings come out Monday.

Among those who expressed their admiration for Williams was Keys, who has said that as a small child she remembers watching Venus on TV at Wimbledon and wanted a white tennis dress just like hers.

''I think Venus has helped the sport,'' said Keys. ''Just watching her is inspirational. She's had her health battles. She loves tennis. She's still out here, and she's doing it remarkably well.''