World number one Nadal, a three-time runner-up in Miami, took just 59 minutes to thrash Uzbek Denis Istomin 6-1 6-0 at the ATP 1000 event.Nadal converted six of seven break points in an impressive display, and the 13-time grand slam champion believes his movement is improving after a back injury suffered in January. "I played a very complete match," he said. "No mistakes, serving with good percentage, and playing a lot of winners. My movements were better than what I did at last events." Despite having never won the Sony Open, he will be looking to reach the quarter-finals for the seventh straight time when he takes on Italian Fabio Fognini. The Italian 14th seed battled past Spaniard Roberto Bautista Agut 4-6 6-3 6-3 in just over two hours. Swiss third seed Wawrinka equalled his best result at the tournament, reaching the round of 16 with a 7-5 6-4 victory over Frenchman Edouard Roger-Vasselin. An entertaining fourth-round meeting with Alexandr Dolgopolov awaits Wawrinka. The Ukrainian 22nd seed recovered from being a break down twice in the third set to get past Serbian lucky loser Dusan Lajovic 3-6 6-0 7-6 (7-5). Dolgopolov is in good form having reached the semi-finals at Indian Wells, and he holds a 2-1 head-to-head record over Wawrinka – although Rome last year was a walkover in his favour. Czech seventh seed Tomas Berdych was untroubled in a 6-2 6-4 victory over Portugal's Joao Sousa. Berdych will meet 10th seed John Isner after the big-serving American sent down 17 aces in a 7-5 6-3 win against Spanish 18th seed Nicolas Almagro. Canadian 12th seed Milos Raonic blasted his way past Spaniard Guillermo Garcia-Lopez 6-1 6-2 in 56 minutes and will meet German Benjamin Becker after the lucky loser was too good for Slovenian qualifier Aljaz Bedene 6-3 7-5.