Roger Federer comfortably beat Jack Sock 6-4, 7-6 (4) in the first round-robin match of the ATP Finals, but not before missing one of the easiest putaways he'll see all week.  
Down 4-2 in the opening set, Sock flubbed a backhand half-volley, giving Federer a short ball from point-blank range. 
Sock, out of options, turned around to use his rear end for protection. But Federer hit the easy forehand right into the net. This gave Sock the game, though he wouldn't go on to win the set. 
"That's a big target, when he turns around," Jim Courier said on Tennis Channel. "There's a lot to hit there."
"It was a big distraction, I'll tell you that," Federer said afterward, "because it was very big. That's what I should have aimed for." 
Then at 4-4 in the second set, Sock took a tweener out of the air that—against anyone but Federer—could have won the point. But the 17-time Grand Slam champion answered with this backhand pass: 

Federer is seeking his seventh career ATP Finals title.