He was past his 30th birthday, they would point out.

About 2½ years went by without any additions to his Grand Slam trophy case, the thinking went.

First Rafael Nadal, then Novak Djokovic, overtook Federer in the rankings and as the man to beat at major tournament after major tournament.

Well, look at the guy now. Wimbledon champion, once again, stretching his record total to 17 Grand Slam championships. Ranked No. 1, once again. And — heading into Monday’s start of the US Open — the favorite to reach the final, once again.

Federer’s pursuit of a sixth US Open title at age 31 will certainly be among the main angles to keep track of on the hard courts of Flushing Meadows.

Other stories to watch include:

■  Djokovic’s bid for a second consecutive championship in New York and fifth major title in two years;

■  Andy Murray’s attempt to follow up his Olympic gold medal with Britain’s first Grand Slam men’s singles title since 1936;

■  Andy Roddick’s hope for one more deep run in front of the home fans;

■  Four-time major champion Kim Clijsters’s farewell to tennis in what she says is the last tournament of her career;

■  Venus Williams’s return to the US Open a year after withdrawing from the tournament and revealing she was diagnosed with an autoimmune disease;

■  Serena Williams’s try for her 15th major trophy — and, of course, what sort of interaction she might have with on-court officials after a foot-fault tirade in the 2009 semifinals, then a ‘‘you’re just unattractive inside’’ monologue in the 2011 final.

‘‘My mind frame this year is that something is going to happen, for sure, because something always happens to me at the Open, whether it’s a horrendous line call that’s 2 feet in or whether it’s a grunt and I get a point penalized or a foot-fault when I actually don’t foot-fault. I’m prepared for something to happen,’’ said Serena, a three-time champion in New York whose serve was dominant recently en route to her fifth title at Wimbledon and two gold medals at the Olympics.

Another key question is what sort of effect there will be from the short turnaround and shift to hard courts after the grass-court London Games.

“There’s no doubt about it: This is not an ideal preparation,” said Federer, routed 6-2, 6-1, 6-4 by Murray in the Olympic final on Aug. 5, less than a month after beating him in four sets on the same court in the Wimbledon final.

Given how rare it is for a man past 30 to remain in the upper echelon of tennis — a not-quite-31 Federer was the oldest Wimbledon champion since Arthur Ashe in 1975 — and the ascension of a couple of rivals in their mid-20s, there were plenty of whispers that the Swiss superstar might be done.

Federer, Djokovic, and Nadal have combined to win 29 of the past 30 Grand Slam titles.

But with Nadal sidelined, and Murray still waiting to win a major final, Federer and Djokovic appear set to take center stage at the US Open.