Buzarnescu made WTA qualifying debut at 2007 Fés. Introduced to tennis at age 4 by parents, she has been part of the Romanian national Tennis federation since 12 and grew up idolizing Pete Sampras and Monica Seles. After a long streak of injuries and a couple of knee surgeries, she considered to leave tennis and gained PhD in sports science from UNEFS in Bucharest. In 2015 she played team competitions in the Netherlands, finding pace and motivations., That year she won 48 matches, four ITF Circuit titles and rose over 600 places in the rankings, finishing at No.260.
In 2016 she posted a 9-11 win-loss record in 2016, with best result a QF run at $50k ITF/Hodmezovasarhely, finishing the season ranked No.351.
In 2017 she took three months off for surgery to her left wrist. She played her first Grand Slam main draw, losing to Caroline Wozniacki in her first match against a Top 50 opponent. In Linz, she lived her breakthrough tournament. She beat fourth seed Anett Kontaveit in straight sets before defeating Alja Tomljanovic and Belinda Bencic in three sets and reached the semifinal in her first WTA main draw appearance. She consequently became the oldest player to make her Top 100 debut since Israel’s Tzipora Obziler in 2007.
She opened the season reaching her first career WTA singles final at Hobart (l. Mertens), having not dropped a set en route to the final. After a first-round exit at Australian Open, Indian Wells and Miami, she lost to Kvitova her second tour-level final in Prague, where she also finished runner-up in doubles (w/Marozava, l. Melichar/Peschke). She finished with an 11-7 record on clay in 2018, as she also moved to the semifinals in Strasbourg (l. eventual R-Up Cibulkova), where she collected her first career doubles title at Strasbourg (w/Olaru, d. Kichenok/Rodionova), and enjoyed a run to R16 at Roland Garros, her best result at a major (l. Keys). She produced one of biggest upsets at this year’s Roland Garros by defeating World No.4 Svitolina in straight sets in the third round.
On grass, she made her Wimbledon main draw debut reaching the third round (l. Karolina Pliskova) in the fourth grass court event of her career at tour-level. Previously, she had made a semifinal run in Birmingham (l. eventual champion Kvitova), sealing her first quarterfinal and semifinal at WTA Premier-level, and advanced to the quarterfinal in Nottingham (l. Osaka) in what was her first-ever WTA-level tournament on grass. In Eastbourne she also reached the round-16 in Eastbourne (l. Ostapenko); her win over No.20 Bertens marked her fourth career win over a Top-20 player.
She posted a semifinal showing at home tournament in Bucharest (l. eventual runner-up Martic) then she won her maiden WTA title in San Jose (d. Sakkari) scoring her fifth career Top 20 win over Mertens en route to it, having previously upset No.6 Ostapenko (2018 Doha), No.4 Svitolina (2018 Roland Garros), No.5 Svitolina (2018 Birmingham) and No.20 Bertens (2018 Eastbourne).
She retired with a right ankle injury during the second round at Montréal, forcing her to miss the remainder of summer hard court season. On return, she suffered two first-round defeats to Sasnovich in Moscow and Beijing.