Guillermo grew up in Madrid, Spain where he learned how to play tennis at the age of 5. In juniors he earned a #100 senior national ranking in Spain and was top 4 in the Spanish national championships and #990 ATP.

He was recruited by Georgia Tech, where he was a three-time ITA All-American and four-time All-Atlantic Coast Conference performer who rose as high as No. 3 in the ITA national singles rankings during his career. ACC Player of the Year in 2011 and the first ACC player ever to also be named ACC Scholar-Athlete of the Year in the same year. Major contributor from his first season at Tech and played No. 1 for the Yellow Jackets. Named 2008 ACC Freshman of the Year and 2008 ITA/Mideast Region Rookie of the Year. Finished his career with a 119-38 record, surpassing the career mark for singles victories at Georgia tech. He majored in Industrial Engineering.

After college Guillermo played in the ATP tour, where he was ranked #840 before getting injured after 10 months of playing. Now he is working for Microsoft as a Consultant while collaborating with the High Performance program.