Novak Djokovic overcame an arm injury to beat Jerzy Janowicz in four sets in the US Open first round.

The world number one and defending champion needed treatment during the encounter on Monday, but came away a 6-3 5-7 6-2 6-1 win.

Djokovic came into the year's last major with a wrist injury, yet seems to have concerns over his arm at Flushing Meadows.

The 12-time grand slam champion took a medical timeout during the first set and his right arm seemed to trouble him throughout the two hours, 37 minutes.

Despite those worries, the Serbian set up a second-round meeting with Czech Jiri Vesely, who won their only previous encounter earlier this year.

Djokovic was there for the taking for Janowicz, the Polish world number 247 who was once ranked 14th before injuries took their toll.

But 2013 Wimbledon semi-finalist Janowicz was unable to capitalise, giving Djokovic complete control of the match immediately after winning the second set.

That was all Djokovic needed as he rolled to victory from then on, despite rarely reaching his lofty heights.

STATISTICAL BREAKDOWN

Djokovic [1] bt Janowicz 6-3 5-7 6-2 6-1

WINNERS/UNFORCED ERRORS
Djokovic – 34/18
Janowicz – 41/59

ACES
Djokovic – 12
Janowicz – 5

BREAK POINTS WON 
Djokovic – 7/20 
Janowicz – 2/12

FIRST SERVE PERCENTAGE 
Djokovic – 62
Janowicz – 54

POINTS WON ON FIRST/SECOND SERVE
Djokovic – 69/63
Janowicz – 63/41

TOTAL POINTS 
Djokovic – 131
Janowicz – 100