Serena Williams won the Australian Open today, defeating her sister, Venus, 6-4, 6-4.

Serena has won more women’s grand slam singles titles in the open era (23) than anyone. And her victory, at age 35, makes her the oldest woman to win a major championship.

A strong case can be made that she is the greatest women’s player in the history of the game.

And it makes me wonder if her successes have led us to disregard what sort of player Venus Williams might have been had her sister taken up another sport.

Venus has won seven major championships. On seven other occasions she reached a major final … only to lose to big/little sister Serena.

Venus was 21 when she worked her way up to No. 1 in early 2002, held that spot for three weeks, did another four weeks at the top in the spring of that year, and four more early in the summer …

Right up till when she lost the final of Wimbledon to … Serena, 20, who also took the world No. 1 spot from her — and held it 57 weeks.

Venus has never been No. 1 again. Eleven weeks in the first half of 2002, and never again.

Another 15 years of mostly elite tennis, for Venus, and not one of those weeks as No. 1.

While Serena sat at the top for a total of 310 weeks — or about six years.

In 2002 and 2003, the sisters met in the championship match of four consecutive major events. Serena won all of them.

By the time that stretch was finished, it was clear who the better player was. As good as Venus was, and she was very good, Serena was better.

Consider Venus’s end-of-season rankings. Until 2002, when Serena took charge, Venus had finished Nos. 5, 3, 3 and 3 in the world. She was No. 2, to Serena, in 2002, and in subsequent years finished ranked 11, 9, 10, 48, 8, 6, 6, 5.

Or 12 years out of 13 where Venus was one of the game’s elite, and winning lesser tournaments, but not the big ones — often because her sister would beat her down.

Her career appeared stalled by a diagnosis of Sjogren’s Syndrome in 2011, when she missed much of the season and fell to 103 in the world, but by the end of 2014 was back up to 19, then 7 and 17.

She was relevant again, and this year she moved up to No. 11 with her run to the Australian final. Where she lost to, of course, Serena.

In their careers, they have met 28 times, with Serena winning 17 of the matches.

Venus won five of the first seven, but it was mostly Serena thereafter.

Venus went from 2001 to 2005 without defeating Serena.

Since 2009, Venus has beaten Serena once, in the Rogers Cup, in nine meetings.

You get the picture. Venus had a very nice career. Without little sister so often dominating the scene, Venus’s career probably would have a lot more major championships on it. Instead of seven, maybe 12 or 13? Instead of 11 weeks as No. 1, 100 or 200?

It seems clear the sisters root for each other. But when they play head to head … only one can win, and that one usually was Serena.

Venus would not be human if she hadn’t thought, and more than once, “What kind of career might I have had if Serena had joined the basketball team?”

And we can answer, “Better, and maybe a lot better.”