Before each day's play at Flushing Meadows, we'll preview and predict three must-see matches.

Maybe it shouldn’t, but it surprises me to learn that Cilic has won his last three meetings with Tsonga, all in straight sets, and that he leads their head to head 4-3. Jo has been the better player for longer, but in the last year he has taken a dip while Cilic has risen into the Top 10. As for this tournament, each has been dominating with his serve. Tsonga has yet to be broken, while Cilic fired 23 aces in four sets against Jeremy Chardy in his last match. Fans at Tuesday’s day session should expect more of the same: Unreturnables, holds, and, most likely, a tiebreaker or three. Tsonga has been to a Slam semi once this year, in Paris, but in his last two matches Cilic has started to remind me of the Cilic who played here in 2014. That’s a pretty good Cilic. Winner: Cilic

The 27th meeting between the Williams sisters may be the most consequential since they faced off in the Wimbledon final six years ago. They played again in the fourth round at Wimbledon this year, which was obviously important, but on Tuesday Venus has a chance to stop Serena’s run toward the ultimate accomplishment, a calendar-year Grand Slam. Serena says there’s no one she’d rather not face; not only is Venus is her sister, but she considers her the toughest player in the draw, period. At 35, Venus is indeed still formidable, as she showed by dismissing teen sensation Belinda Bencic in the third round. But Serena seems to have reached her second-week form, which has historically made her unbeatable. She’s equally tough to beat when she takes her opponent with the utmost seriousness, and there’s no opponent she’ll take as seriously as her big sister. Winner: S. Williams

“I don’t know what I’m going to do against him.” That’s essentially what Lopez said when he was asked after his last match to contemplate facing Djokovic in the quarterfinals. Hopefully Feli has figured out some type of game plan, but you could see why his first reaction would be confusion: Djokovic has won all five of their meetings, with the loss of just one set. One positive, as far as the 33-year-old Lopez is concerned, is that he hasn’t lost to Djokovic since 2012. Since then, he's played some of the best tennis of his career. But not as good as Djokovic. Winner: Djokovic