United's misfiring Chilean forward scored the third as his nation began their Copa America defence with a thumping 4-0 win over guest participants Japan last night.
The 30-year-old, who pockets £505k-a-week at Old Trafford, has not found the net since January 25 in the FA Cup against Arsenal.
Sanchez told reporters: “For six weeks I felt worse than I ever have before.
“I struggled in the first half as I felt stifled but in the second half I was more relaxed and played with more freedom and excitement."
While his nation winning the last two Copa America crowns, the United flop insists he and his team-mates are on the right track to make it a treble.
The ex-Arsenal man said: “I think we have improved as a team since 2015 in defending and getting on the attack quickly.
“We've won a very difficult game and now we have to think about our next one."