Roger Federer overcame a stern test from Alexander Zverev to progress to the semi-finals of the ATP Finals with a three-set win on Tuesday.
With Jack Sock having beaten Marin Cilic earlier in the day, the Australian Open and Wimbledon champion knew he would clinch a place in the last four with victory,
Zverev has charged sharply up the rankings and now sits at third in the world, and the 20-year-old's contest with the 19-time grand slam winner was billed as a battle between the master and the apprentice.
It was the master who prevailed on this occasion, but only after he had received a significant examination from the German in what was the fifth match out of six at the season-ending showpiece to go the distance, with Federer eventually prevailing 7-6 (8-6) 5-7 6-1.
Zverev now must win his final clash in Group Boris Becker with Sock to seal his spot in the last four.
If an illustration of the challenge Zverev presents was needed, it was provided when Federer was forced to save three break points in the opening game, the Swiss then seeing one go begging in the subsequent game.
The fact that an exasperated Federer shouted, 'Come on!' as early as the fifth game after winning a point to go 40-30 ahead was a further compliment to Zverev, who summoned his resolve to withstand a late barrage, saving two set points in his last service game to force a tie-break.
He then raced into a 4-0 lead in the breaker, only for Federer to rattle off eight of the next 10 points - saving a set point in the process - to forge ahead.
Federer hit 17 winners to his opponent's 10 in the first set and it looked as if he would canter to a routine victory when he broke in the first game of the second courtesy of a lifeless Zverev drop shot before holding to love.
But again Zverev's admirable resilience came to the fore, a poor Federer volley giving him enough room to nail a forehand down the line and get the set back on serve.
Some strong serving and a deft backhand volley stopped Zverev from claiming the double break at 4-3 up, but Federer's backhand escaped him in the final game of the set.
Zverev surged into a 40-0 lead and, after seeing two break points squandered, clinched the third when Federer sent a cross-court shot wide at the end of a superb rally.
However, an errant cross-court backhand from the 20-year-old gave Federer the initiative and a 2-1 lead in the third, and this time there was no way back.
The double break came in short order as Zverev's forehand fell apart in the fifth game and, though Federer's serve came under some pressure in the next, he made no mistake in progressing to the semis for the 14th time in 15 tournament appearances.
Federer  bt Zverev  7-6 (8-6) 5-7 6-1
Federer – 26/38
Zverev – 20/45
BREAK POINTS WON
Federer – 4/8
Zverev – 2/11
FIRST SERVE PERCENTAGE
Federer - 53
Zverev - 63
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Federer - 83/54
Zverev - 73/43
Federer - 109
Zverev - 96
|U.S. Open champion Koepka happy to continue being ´overlooked´|
|Pogba: I´m the most criticised player in the world|
|Maradona: Sampaoli´s game plan against Iceland was a disgrace|
|De Gea will bounce back from error – Marchena|
|Slater named for Maroons return|
|Woods, Faldo, Harrington and Koepka – U.S. Open champion joins fine club after successful defence|
|Fleetwood positive despite falling short at U.S. Open|
|Jesus: I had no reason to play for a penalty|
|Hernandez admits to exaggerating fouls against Australia|
|Koepka says winning two U.S. Opens not even in his ´wildest dreams´|
|Hernandez: Griezmann an idol at Atletico|
|Sri Lanka take charge despite Gabriel exploits|
|U.S. Open final-round timeline: How clinical Koepka kept his crown|
|Koepka fights off challengers to successfully defend U.S. Open title|
|´Aching´ Neymar urges referees to intervene|
|BREAKING NEWS: Koepka holds on to defend U.S. Open title|
|Lozano goal causes artificial earthquake in Mexico|
|Djokovic: Mental battle will be Murray´s biggest|
|Hummels criticises Germany tactics in Mexico loss|
|Brazil the latest favourites to stumble, but Tite and Neymar won´t panic|
|Magnificent Fleetwood matches U.S. Open record with closing 63|
|Brazil 1 Switzerland 1: Zuber pegs back below-par Selecao|
|Warrington hold off Wakefield fightback, Tigers held despite Hitchcox heroics|
|Germany follow trend of poor starts for World Cup champions|
|Reed on the charge as U.S. Open race hots up|
|Milinkovic-Savic can play for any team in Europe, says Crespo|
|Southgate keen to unleash his bold new England|
|Konta fumes as Barty takes Nottingham title|
|Kante hails Pogba´s match-winning contribution|
|Germany struggle with generation gap|
|Neymar to make first competitive start since February in Brazil´s World Cup opener|
|Kane gunning for Ronaldo hat-trick heroics in England opener|
|Balotelli would fit in at Marseille - Raiola|
|Captain Ki happy to get tough on South Korea|
|Senegal call up Mbengue with Ciss ruled out|
|Mickelson celebrates at scene of Saturday meltdown|
|Germany 0 Mexico 1: Lozano stuns woeful reigning champions|
|Chandimal to face hearing after pleading not guilty to ball tampering|
|Griezmann ´must do more´, says Deschamps|
|Gasquet shows his class on grass to end Chardy´s chances|
|Courtois: Belgium outsiders not World Cup favourites|
|You can´t compare Ronaldo and Messi – Adrien Silva|
|Kiwis name seven uncapped players for England Test|
|Lorenzo tells critics: Remember MotoGP wins next time I struggle|
|Maaloul singles out ´future of English football´ Alli as main threat|
|Poland v Senegal: Nawalka waits on Glik|
|All Blacks draft in Riccitelli and Hemopo, Barrett not risked for third Test|
|Palermo to appeal play-off result after ´illegal game´|
|Once a year is not enough! - Alonso loved Le Mans bow|
|Colombia v Japan: Kawashima eager to right the wrongs of 2014|
|Russia v Egypt: Salah poised to derail hosts´ juggernaut|
|South Korea swapping kit numbers to confuse Sweden|
|Neuer, Ozil start for Germany in World Cup opener|
|Costa Rica and Serbia serve up plenty of the spectacular in sunny Samara|
|Alonso edges closer to ´Triple Crown´ with Le Mans glory|
|Costa Rica 0 Serbia 1: Kolarov stunner seals points|
|Belgium are better than Argentina – Gomez and Panama ignoring Iceland result|
|Messi, Ronaldo or Neymar would keep the goal - Evra defends Pogba|
|Two in a row for dominant Lorenzo in Barcelona|
|Maradona denies racism claim|
|Resilient Krunic breaks Tour duck|
|Federer wins Stuttgart Open on his return|
|Injured Vunipola to miss England´s series finale in South Africa|
|Ibrahimovic not involved in Sweden´s World Cup plans, insists Andersson|
|Sri Lanka captain Chandimal charged with ball tampering|
|Portugal will not underestimate Morocco, vows Adrien Silva|
|Messi is not Maradona, he does not win a World Cup alone - Crespo|
|Hourcade resigns after Pumas´ series defeat|
|Second place is worthless - Rivaldo admits pressure is on Neymar and Brazil|
|South Africa character made up for mistakes - Erasmus|