Spanish teenager Carlos Alcaraz reached his first Grand Slam final with a five-set win over American hope Frances Tiafoe in the US Open semi-finals.

Third seed Alcaraz won 6-7 (6-8) 6-3 6-1 6-7 (5-7) 6-3, while fifth seed Ruud earned a 7-6 (7-5) 6-2 5-7 6-2 victory.

Whoever triumphs in Sunday’s final will become the new men’s world number one.

The champion will replace Russia’s Daniil Medvedev, who lost in the last 16 at Flushing Meadows, at the top of the ATP rankings.

Alcaraz outlasts Tiafoe to win another epic

Alcaraz has long been touted as a potential Grand Slam champion and now is one victory away from becoming the youngest man to win a major since Rafael Nadal at the French Open in 2005.

The teenager secured the opportunity by coming through another epic contest that showed his talent, athleticism and heart.

Beating 22nd seed Tiafoe, which took him more than four hours and four match points, was the third match in a row where he won a lengthy five-setter.

Tiafoe, 24, was aiming to become the first American man to reach a US Open final since Andy Roddick in 2006, taking the lead on his fifth set point in the opener when Alcaraz produced a double fault.

Alcaraz had not previously dropped the first set in the tournament, but fought back to lead by winning 10 of 12 games going into the fourth set.

Looking flat and weary at this stage of the match, Tiafoe twice fell a break down early in the fourth. But he recovered both breaks to re-energise himself – and the crowd – then saved a match point at 5-4 with a nerveless drop shot.

Tiafoe had won all seven previous tie-breaks he had played at Flushing Meadows this fortnight – equalling a record set by Pete Sampras in 2000 – and made it eight to ensure there would be a deciding set.

After coming back from 2-0 down, Tiafoe hit a double fault to lose his serve for 3-2 and Alcaraz seized the initiative.

An inch-perfect lob from the Spaniard had helped turn the fifth game and he produced another to bring the fourth match point which he converted when Tiafoe hit a backhand into the net.

Ruud earns another shot at winning first major

Ruud, 23, has another chance of landing a first Grand Slam title three months after losing to Nadal in the French Open final.

The world number seven, who has won eight of his nine tour titles on clay courts, says he has been “surprised” by his run at the final major tournament of the season.

Ruud’s performance at Roland Garros cemented his reputation as a clay-courter but, having reached the Miami final in April and the Montreal semi-finals last month, he has again shown he has the ability to be successful on the North American hard courts.

Against Khachanov, an edgy start saw both players break for the lead in the first set, but fail to consolidate and immediately allow their opponent to level.

That led to a tie-break in which Ruud clinched the opener by winning a 55-shot rally with a beautiful backhand down the line.

Showing a lack of nerves in such a key moment proved pivotal in the outcome of the match.

Ruud served superbly in the second set, not dropping a point in his service games, and moved into a two-set lead by breaking 27th seed Khachanov twice in quick succession.

Khachanov, who played at a consistently high level to beat Australia’s Nick Kyrgios in the quarter-finals, improved in the third set and extended the match when he broke Ruud in the 12th game.

But Ruud quickly regained control. A running forehand winner on break point put him into a 2-1 lead in the fourth set, giving him the momentum to take Khachanov’s serve again for 4-1 and then clinically close out victory.