Pernfors played a topspin-heavy baseline game with a double-handed backhand, like his countrymen Björn Borg and Mats Wilander, but he lacked their consistency and relied on a crowd-pleasing game full of variety, liberally employing the drop shot and the topspin lob. In 1986 Pernfors reached his first (and only) Grand Slam singles final at the French Open. He defeated Boris Becker in the quarter-finals and Henri Leconte in the semi-finals.
In the final he lost in straight sets to then World Number.1 Ivan Lendl 6–3, 6–2, 6–4.
The following year at Wimbledon he again lost a two-set lead, falling to Jimmy Connors 1–6, 1–6, 7–5, 6–4, 6–2 after having led 6–1, 6–1, 4–1, and afterwards 3–0 in the fourth set. His second came just a month later in Scottsdale, Arizona.
In the fourth round of the Australian Open in 1990, Pernfors faced John McEnroe during a match in which McEnroe became the first player to be disqualified under a new Code of Conduct that had recently been introduced in tennis. Pernfors lost in the next round, the quarterfinals.
Injuries limited Pernfors" performances on the tour in the first few years of the 1990s.
A few weeks later he pushed Wilander to five sets in the second round of the United States. Open, falling 7–6, 3–6, 1–6, 7–6, 6–4. His career-high singles ranking was World Number. 10 in 1986. His career prize-money earnings totalled $1,363,793.
In addition to Becker, Agassi, McEnroe and Martin, Pernfors holds victories over Wilander, Pete Sampras, Stefan Edberg, Jim Courier, Thomas Muster, Sergi Bruguera and Michael Stich.
Since retiring from the tour, Pernfors has been a regular competitor in seniors events. Grand Slam finals
= Singles: 1 (0–1) Masters Series finals
= Singles: 1 (1–0) finals
Singles: 5 (3–2)
Wins (3)
Doubles: 3 (1–2)
Wins (1).