Rattling a few 136 mph second serves, Milos Raonic struck with the power of a man swinging to remodel the back wall. Then he raced to net and slid a forehand drop shot winner with such subtlety Steve Johnson seemed to wince in surprise at the fluttering ball.

When he wasn't busy booming his punishing serve off the back wall, Raonic stung Johnson with some timely forward thinking. The Canadian clubbed 16 aces, did not face a break point and attacked at the right times charging into the Citi Open semifinals with a 7-6 (2), 6-2 victory.

Johnson had withstood a combined 56 ace in edging towering ATP ace leaders John Isner and Ivo Karlovic in successive third-set breakers to advance to his fifth quarterfinal of the year. The 68th-ranked American immediately went to work on the Raonic serve, snatching a 0-30 lead moments into the match and pressing the Wimbledon semifinalist in a challenging eight-minute game that Raonic finally ended with an ace out wide. Raonic sealed his following two service games with aces.

Both men tried to impose their serves and forehands, command the center of the court and force the opponent to hit his weaker backhand wing from defensive spots on court. The returner's only other threat of the set came in the sixth game. Johnson ended the uprising crunching a forehand winner crosscourt and lining the stripe with an ace for 3-all.

Tie breakers can evoke tension, but Raonic played with more clarity — and confidence from the 18-8 tiebreaker record he carried into the extra session. Accelerating through his returns, Raonic ripped a forehand to draw the error for the mini break for 2-1. The second seeded backed it up with an ace and a crackling serve out wide, stretching the lead to 5-1 when a Johnson forehand sailed long. Throughout the match, Raonic's slider wide on the deuce side set up his inside-out forehand. He used that combination again to earn set point and smacked his 11th ace to seal the first set — winning his fifth straight breaker of the week.

Working with coaches Ivan Ljubicic and Ricardo Piatti, Raonic has tried to take advantage of his explosive serve — and pressure opponents — by moving forward more. He picked the right time to attack, anticipating the angle and feathering that forehand drop volley for the first break point of the match. A rattled Johnson missed the mark on an inside-out forehand Raonic had the break and a 1-0 lead to start the second set.

The scary thing about Raonic is he has even more upside to his game: His second serve can get sharper, he can spread the court more effectively if he varies his predictable inside-out forehand pattern a bit and if he can commit to moving forward he can lessen the stress on his body. He can also use the body serve more to piercing effect.

A 136 mph second serve into the body serve set up forehand down the line as Raonic held at love for 3-1. Johnson put a forehand into the middle of the net, dropping his head in disgust at the miscue, handing Raonic a second break and a 5-2 second-set lead. Closure came with complications: Raonic blew three match points,including a massive 140 mph second serve that was long but ended the 79-minute match with his 16th ace out wide—barely a hair out of place.

The world No. 7 will face 73rd-ranked American Donald Young, who reached his first ATP semifinal in nearly three years with a 3-6, 7-6 (3), 6-2 triumph over seventh-seeded Kevin Anderson.