Reilly Opelka shows off new swing in Citi Open-er
The towering American has been tinkering with his forehand in the hopes of rounding his game into something entirely unbeatable.
The American veteran overcame countrywoman CoCo Vandeweghe at the Mubadala Silicon Valley Classic.
The fourth-seeded German will face Novak Djokovic on Friday, with a place in the gold-medal match at stake.
Gilbert began working with the rising American star when he was just seven years old.
The Canadian can redline his game with the best, but fewer errors have propelled his semifinal push.
"The grass has definitely become slower over the years which is conducive to a lot more baseline play," Russell added.
The Austrian was forced to retire from his Mallorca opener against Adrian Mannarino.