Roger Federer will return to the top of the ATP rankings for the first time since November 2012 after recovering from a set down to beat Robin Haase 4-6 6-1 6-1 and reach the Rotterdam Open's last four.

The Swiss maestro earlier this month confirmed that he had accepted a wildcard to the tournament, which he has won twice, and a run to the semi-finals means he will usurp Rafael Nadal when the ranking are updated on Monday.

It caps a truly sensational 14 months for Federer, whose star appeared to be on the wane when knee and back troubles saw him miss the second half of 2016 and left him 17th in the rankings by January last year.

But Federer has since overseen a scarcely believable new era of dominance, and his triumph at last month's Australian Open was his third victory at the last five grand slams, and his 20th major in total.

At 36, Federer - who initially struggled to get to grips with his opponent's gutsy play before dominating proceedings - replaces Andre Agassi as the oldest man to top the rankings and will extend the record of 302 he already holds for the most accumulative weeks at the summit.

It looked ominous for Haase when Federer engineered three break points in game two of the first set, but the Dutchman staved off the threat with some gritty play and a big ace.

From there it was Haase who was more willing to take risks, and - despite seemingly having missed a chance with an ill-advised lob - it was the underdog that broke for a 5-4 lead with a driven forehand.

That was the first time this week Federer had faced break points, and Haase finished off the job with a mammoth ace to clinch the opener.

But Haase failed to build on the momentum, as a poorly time forehand gifted Federer three break points that he converted with a volley at the net for a 2-0 second-set lead.

Haase was in trouble on serve again in game six and a long forehand meant the writing was on the wall for the second set.

The pattern continued at the start of the decider as Federer broke immediately with a breath-taking backhand pass from the baseline, and more textbook play opened up a double-break 3-0 lead.

It was now one-way traffic and new world number one Federer celebrated victory when Haase double faulted when trailing 5-1.