Born and residing in Prague, where she trains at the TK Neride Club, Denisa Allertova was introduced to tennis by her grandmother, the former professional tennis player Blanka Politzerova who played against Martina Navratilova, and her mother, Camila, is a kids' tennis coach. She played the first event of her career on ITF Circuit in Czech Republic in 2008. She continued to play at ITF level winning her first title at $10k event in Antalya in 2012. She added a further title in 2013 in Sharm el Sheikh and seven in 2014: two in Antalya, others in Budapest, Siofok, Plzen, Alphen A/D Rijn and Istanbul, the biggest and only $50k title in her ITF career.
She made her WTA main draw debut at 2014 Luxembourg (as a qualifier), upsetting Top 40 players Lisicki and Lepchenko en route to the semifinals.
In 2015, she reached the first WTA singles final in Guangzhou, defeating No.2 Halep in the quarterfinals (l. Jankovic). She reached two quarter-finals that season, in Prague (l. eventual champion Karolina Pliskova) and Linz (l. Flipkens).
She posted her career-high ranking of No.55 the week ok March 21, 2016. That year reached the semifinals in Tashkent (l. Hibino) and the quarterfinals in Linz (l. Suárez Navarro) and Luxembourg (l. Bertens), all back-to-back. She also made the third-round at Indian Wells in March (l. Konta), in her main draw debut at WTA Premier-mandatory tournament. At Grand Slam level, she moved to the third-round for the first time at Australian Open and during the US Open she defeated Ivanovic in the final match of the former No.1’s career.
She ended 2017 at No.122, down from career-best No.63 in 2015 and No.93 in 2016. She reached the second-round at Wimbledon (l. Martic), US Open (l. Osaka), Seoul (l. Hogenkamp) and Tashkent (l Babos). Other highlights included the tenth career title at ITF level at $60k event in Zhuhai (d. S.Zheng in F)