There was nothing subtle about last night's Williams-Williams U.S. Open match, the rare occasion when an argument between sisters becomes riveting spectator sport.

Contrary to suggestions by a couple of sports-talk radio hosts Tuesday, that Venus Williams would not dare attempt to derail younger sibling Serena's quest for a Grand Slam sweep, both of the Williamses provided the enthralled Arthur Ashe Stadium crowd with a duel of such power and passion that it didn't resemble the rest of the women's tennis played in this tournament, or any other.

The more accomplished of the two, Serena, predictably pulled away for the 6-2, 1-6, 6-3 quarterfinal win. But not until she and Venus again demonstrated their combined ability to put the entire sport on Williams Standard Time and their well-established individuality.

Not just a tennis tag team of dominance, with a combined 28 major-tournament titles, the two are noticeably distinct: One an embodiment of nobility, Venus. The other, power. On one side, the long-limbed, slender and measured presence. On the other, Serena, the sturdy, compact, emotive one.

Tennis author Peter Bodo once described the distinction between the two as "almost like a high jumper and a heavyweight fighter.''

Whether the celebrity-heavy crowd, including a certain controversial presidential candidate, came to be seen as much to see, the sisters filled every one of Ashe's 23,771 seats before warmups and kept them there.

advertisement | advertise on newsday

Outside the stadium, in the south plaza, hundreds watched the giant video screen. Venus and Serena bludgeoned serves, flicked drop shots and lofted lobs, walloped ground strokes and didn't hesitate to use video challenges.

"I can't imagine playing my sister,'' said Samantha Stosur, who beat Serena in the 2011 Open final. "If I had a sister.''

Roger Federer said, "I'd have a hard time playing a brother,'' though he doesn't have one. Novak Djokovic, making his admiration for the sisters clear, said he still found it "hard to watch'' them battle each other.

In their separate friends' boxes, there was little applause, apparently out of fear of showing favoritism within the family, while their mother had insisted she would not watch the match.

Early in their careers, their battles were messily played, disorienting psychological studies, but that long since gave way to a fascinating athletic narrative. And anyone who thought that either sister was not trying her best Tuesday night was just not paying attention.