Alexander Zverev advanced to his fifth final of the ATP Tour season after upstaging second seed Kei Nishikori at the Citi Open, where he will face Kevin Anderson in the decider.

Highly-rated German and fifth seed Zverev was too good for Nishikori, triumphing 6-3 6-4 in Washington on Saturday.

Victorious in Montpellier, Munich and Rome this year, while he lost to Roger Federer in Halle, Zverev has the chance to add another title to his growing collection on Sunday after winning 94 per cent of his first services points.

The 20-year-old did not face a break point against the Japanese star, converting two of his own after a little more than an hour on court.

Standing in the way of Zverev is South African Anderson, who overcame home favourite Jack Sock 6-3 6-4.

Anderson sent down 12 aces and saved all five break points as he reached his first final since claiming the Winston-Salem Open in 2015.

"It feels great. It's great to get another match win," Anderson said. "It was definitely a tough match. I felt I did quite a few things well today, couple things I thought I could have done a little bit better. But most importantly I was able to get the win and give myself a shot at the title tomorrow.

"It's a great start to the summer. It's obviously a very big tournament so I'm very pleased to be through to the finals."