Novak Djokovic says his "wolf energy" helped him defeat a spirited Denis Kudla to move one step closer to retaining his Wimbledon title.

American qualifier Kudla, a strong grass-court player, had held a 4-1 lead in the third-set tie-break but let his advantage slip.

Djokovic credited his upbringing for his fighting, animalistic instinct.

"Part of it is genes, my family, the way I have grown up during difficult times in the 90s for my country," he said, referring to the Nato bombings of Belgrade during the Kosovo War.

"Failure was never an option for me or my family, we had to find a way to fund the basic needs to survive.

"I spent a lot of time in the mountains with wolves and this is wolf energy there. I am not kidding."

He added: "I have to give credit to Denis for playing really well.

"The third set was very close. He's a great guy on and off the court, we get along really well and I wish him all the best.

"He played a great three sets today, he was a bit unlucky in the tie-break, he was in front for most of it. I somehow found the way to win."

Djokovic - chasing a record-equalling 20th major - is now the first man to win at least 75 matches in all four Grand Slams.

Elsewhere, Russian fifth seed Andrey Rublev needed almost three hours to defeat Italian Fabio Fognini.

Rublev won 6-3 5-7 6-4 6-2 to reach the Wimbledon fourth round for the first time, and he will play Hungary's Marton Fucsovics next after he defeated ninth seed Diego Schwartzman.

Rublev is one of two Russians to reach the fourth round, with Karen Khachanov also progressing with a 6-3 6-4 6-4 win over Frances Tiafoe.

Roberto Bautista Agut, a semi-finalist at SW19 in 2019, battled to a 7-5 6-1 7-6 (7-4) victory against Dominik Koepfer.

He will play the winner of Friday's Centre Court meeting between Andy Murray and 10th seed Denis Shapovalov.

Djokovic's next opponent, 17th seed Garin, is the first Chilean to reach the Wimbledon fourth round in 16 years after his four-set win over Pedro Martinez of Spain.

The last Chilean to reach this stage was Fernando Gonzalez, who went on to the quarter-finals in 2005.