Roger Federer felt fans who booed Alexander Zverev at the O2 Arena were out of order after the German secured his place in the ATP Finals decider and denied him a 100th singles title.
Zverev stopped mid-rally during a second-set tie-break when a ball boy in his eyeline dropped a ball with Federer leading 4-3.
A Zverev ace flashed past Federer when the point was replayed and the Swiss soon bowed out with a 7-5 7-6 (7-5) defeat in London.
The crowd voiced their disapproval after Zverev halted the point and he apologised after he was also booed and jeered during his on-court interview, but Federer said the third seed did not need to apologise.
Federer said: "He apologised to me at the net. I was like, 'buddy, shut up! You don't need to apologise to me here. Congratulations on a great match and a great tournament so far.'
"He didn't do anything about it. He just called it how it was. He felt it affected play. There is a rule that if something like this happens, obviously you replay points."
The 20-time grand slam champion added: "Look, I understand the frustration. It's just unfortunate circumstances,
"Booing, I never like it. We see it in other sports all the time, but in tennis it's rare.
"So when it happens, it gets very personal and we take it very direct. I think it's unfortunate that this happened. Sascha doesn't deserve it."
Federer said his season will go down as a success despite a disappointing finish.
"I must tell you I'm very proud that at 37 I'm still so competitive and so happy playing tennis." said the Swiss.
"From that standpoint, as disappointed as I might be about this match, if I take a step back, I'm actually very happy about the season,
"It's been a historic season in some ways. Got back to world number one. For me, that was a huge moment in my life, to be honest, in my career because I never thought I would get there again."
|Mourinho is so strong - Guardiola backing for fallen rival|
|Mourinho? Ausilio dismisses Inter return after United sacking|
|Whyte needs to raise his game to beat Chisora again - Haye|
|Brussino leads late Tenerife rally as Venezia down Holon|
|Orleans 1 Paris Saint-Germain 2: Super sub Diaby sends holders through|
|Leicester City 1 Manchester City 1 (1-3 on penalties): Muric stands tall in poor shoot-out|
|Middlesbrough 0 Burton Albion 1: League One side reach semi-finals|
|Bologna 0 AC Milan 0: Bakayoko sent off as Inzaghi claims point against former side|
|Fortuna Dusseldorf 2 Borussia Dortmund 1: Bundesliga leaders suffer shock first loss|
|Rivera yet to make a call on sitting Panthers QB Newton|
|Pulisic would thrive in Premier League, but Berhalter expects Dortmund stay|
|Raptors coach Nurse fined by NBA for criticising referees|
|Solari ´loves´ struggling Real Madrid star Isco|
|Mourinho sacked: Pogba, Lukaku, Fred and his other Man United signings rated|
|Mourinho sacked: What does it mean for Manchester United players?|
|Ibrahimovic provides short-term pain, long-term gain for US - Berhalter|
|River Plate 2 Al Ain 2 (aet, 4-5 on penalties): Perez misses decisive spot kick|
|De Bruyne and Aguero back for City, surprise debut for Garcia|
|Uncapped Varun ´panicked a little´ after huge IPL deal|
|Replays scrapped for FA Cup fifth round|
|Pochettino readies big guns for Gunners|
|Ex-Wasps star Wade struggling with NFL transition|
|BCCI rejects ´baseless´ claims over Kohli-Paine ´banter´|
|Ibrahimovic re-signs with LA Galaxy for 2019|
|Mourinho sacked: Solari not worried for Real Madrid job|
|Mourinho sacked: 895 days and more than £700,000 in five-star luxury|
|ES Tunis 1 Guadalajara 1 (6-5 on penalties): Dhaouadi holds nerve to settle ill-tempered affair|
|Murphy lands permanent Tigers role|
|Mourinho sacked: Real Madrid´s Marcelo lauds ´great coach´ after United exit|
|Unadkat, Varun the top buys at IPL auction|
|Emery prepared to give youth a chance in north London derby|
|Tottenham extend Vertonghen contract until 2020|
|Panthers safety Reid receives seventh random drug test of 2018|
|Kovac relishing Klopp challenge in Champions League|
|Bancroft to return, teenager Lamichhane to fly the flag for Nepal in Big Bash|
|Liverpool still have plenty of work to do - Klopp|
|Messi ´never imagined´ his success after winning record fifth Golden Shoe|
|WATCH: Timberwolves´ Gibson tries to block shot with his trainer|
|Mourinho sacked: Klopp praises departed Manchester United boss|
|Mourinho sacked: Jose the best Manchester United manager since Ferguson - Gerrard|
|Mourinho sacked: Ferdinand calls for ´fresh ideas´ at Man United|
|Mourinho sacked: The mystique has gone as United spell ends in divorce|
|´He´s an interest not only for us but for many´ - Zola praises rumoured Chelsea target Wilson|
|Mourinho sacked: Pochettino focused on Spurs amid Manchester United rumours|
|Mendis eyes double-century for departing Samaraweera|
|Mourinho sacked: Zola expects Jose to be in another job ´soon´|
|Mourinho sacked: Five reasons it went wrong at Manchester United|
|Mourinho sacked: Jose´s Manchester United record in Opta stats|
|Mourinho sacked: Pogba, Ronaldo and Jose´s biggest bust-ups|
|Mourinho sacked: Blanc, Solskjaer - the men who could steady the United ship short-term|
|Mourinho sacked: The football world reacts|
|Mourinho sacked: What former United stars said after Liverpool loss|
|Mourinho sacked: Where next for the axed Manchester United boss?|
|UEFA to investigate alleged racist incidents at Vidi-Chelsea|
|Australia unchanged for rest of India series|
|Mourinho sacked: Pogba´s tweet a dig at departing Man United boss?|
|Newton left frustrated by shoulder injury as Panthers lose again|
|Mourinho sacked: Pochettino & Zidane lead potential Man Utd replacements|
|Mourinho sacked: Neville urges Man United to go for Pochettino|
|Boylen pleased to see Bulls react to red rag in Thunder fracas|
|Icardi and Inter ´very far´ apart in contract negotiations|
|Mourinho leaves Manchester United|
|Curry humbled by latest milestone|
|Robertson: ´Unbelievable´ Alisson will bounce back from error|
|Curry scores 15,000th regular-season point in Warriors win|
|Rams star Gurley ´day-to-day´ with knee inflammation|
|Saints poised to clinch NFC top seed after topping Panthers|
|Mathews, Mendis centuries frustrate New Zealand|
|Kohli: Relentless Australia deserved victory|
|Relief for Paine and Australia after ending Test drought|