#4 Dominic Thiem
Austrian Dominic Thiem is the current World No. 5. He has won eight ATP titles in his career and reached his first Masters 1000 final in 2017. He has beaten each member of the Big 4 at least once. He beat Nadal on clay at the quarter-finals of the 2017 Rome Masters after losing to Nadal in the finals of the 2017 Barcelona and Madrid Opens.
His best showing at the Grand Slams are semi-final losses at the French Open in 2016 and 2017 where he lost to the eventual champions, Djokovic and Nadal respectively. He knocked out defending champion Djokovic in 2017.
He is primarily a baseline player and his best surface is clay. Thiem is comfortable on hard courts as well. He will be looking to improve on his 4th Round appearance at the Australian Open last year.