[2] Apostu-Efremov made his ATP main draw debut at the 2002 Romanian Open in the doubles event partnering Răzvan Sabău.

[1][additional citation(s) needed] As a result, he had a chance to get a university scholarship in the USA; however, he decided to keep playing tennis, and he was one of the top 500 in the world by the age of 20.

[1][additional citation(s) needed] At about the age of 23, Apostu-Efremov suffered a severe injury on his left leg which prevented him from playing for one-and-a-half years.

[6] Apostu-Efremov has known Halep since she was a teenager, and as of January 2020, he has also spent five years coaching Irina-Camelia Begu.

[7] Apostu-Efremov has also trained Mihaela Buzărnescu, Raluca Olaru, Elena Bogdan, and Radu Albot.