The multiple grand slam champion, who needed just 56 minutes to beat his fellow Serb Dusan Lajovic 6-0, 6-1 in the first round of the Association of Tennis Professionals Tour event, also said that he was playing without pain for the first time in two years following surgery to cure the right elbow problem which had kept him off the court for the last six months of 2017.

“It was a great start to the tournament,” Djokovic said afterwards.

“Considering I haven’t played many matches I thought I played well.”

Djokovic, who said nevertheless that he has no agreement to continue working with Vajda after this tournament, has won only two minor titles in the last 20 months.

He has had a particularly turbulent time since parting company with his entire coaching team, including Vajda, after this tournament last year.

The former world number one began working with Agassi at last year’s French Open but was struggling with his elbow problem and did not play again after Wimbledon.

On his comeback at the Australian Open in January Djokovic suffered more elbow pain when losing to Hyeon Chung in the fourth round.

He subsequently had surgery, but looked out of sorts when he made another comeback last month, losing to Taro Daniel and Benoit Paire in his opening matches in Indian Wells and Miami respectively.

Djokovic admitted that he might have returned too quickly following the operation.

“The elbow was not as good as it has been in the last seven days,” he said.

“After two years I can finally play without pain.”

Meanwhile world number 51 Jared Donaldson was involved in an angry confrontation with an umpire after disagreeing with a call during his first round defeat by Albert Ramos-Vinolas.

The 21-year-old American became outraged when a serve by the Spaniard was called in by umpire Arnaut Gabas

Donaldson was seen shouting in Gabas' face after calling him on to court.

Video replays later showed Donaldson was correct but Hawkeye was not in use.

 Donaldson eventually lost 6-3, 6-3 and apologised to his opponent for his behaviour, but refused to shake Gabas's hand.

Gabas was the umpire who suffered an eye socket fracture last year when Canada's Denis Shapovalov sent a ball into his face while venting frustration during the Davis Cup match against Britain.