The Maria Sharapova Express steams on as victories and earnings pile up

Ruthless world No 2 has dropped only five games in her four matches and now faces compatriot Makarova in quarter-final

Maria Sharapova serves during her win over Kirsten Flipkens (EPA)

If there is one player in the women's draw here at the Australian Open who will not be paying too much attention to her prize money it is Maria Sharapova. The world's highest-earning sportswoman banks an estimated $28m (more than £17m) a year, of which the money she earns on the court is all but insignificant.

The 25-year-old Russian has a smart eye for business, however, and the rate at which she has been earning here over the past week is probably matching any of her other commercial interests, including the "Sugarpova" sweets – selling at a handsome $5.99 (£3.70) a bag – which she launched three days before the tournament started.

Sharapova has been on court for just 249 minutes in her first four matches and by reaching the quarter-finals has already guaranteed she will leave Melbourne Park with a cheque for $Aus250,000 (£166,000). Or to put it another way, she has been earning at the rate of $Aus1,000 (£660) a minute.

The Sharapova Express showed no sign of slowing down yesterday as the world No 2 reached the quarter-finals with a crushing 6-1, 6-0 victory over Belgium's Kirsten Flipkens. She has dropped just five games in her four matches, a record for the Australian Open. The only player who has bettered that at any Grand Slam tournament is Mary Pierce, who lost just four games en route to the quarter-finals of the French Open in 1994.

Sharapova's progress is all the more remarkable considering that she arrived here without any competitive matches under her belt, having had to withdraw from two build-up tournaments because of a sore collar- bone.

Despite her lack of on-court time, Sharapova said she saw no need to step up her work on the practice court. "I'm horrible in practice most of the time," she said. "I'm like 'that's a great sign', because I come to the matches and my expectations are quite low. But it depends. Every Grand Slam that I've won or done well at, I've always felt different actually.

"Sometimes I feel like I'm not playing my best tennis in the beginning, but I start playing better. And then a couple that I've won, I felt like I was playing great from the beginning and I was able to carry that through the whole tournament."

Sharapova believes that the work she did in the off-season was more important than anything she might have done in a warm-up event.

"The work that you put in before the tournament is the most important," she said. "What you do in the off-season, you're not going to put this work in during the tournaments. I actually love coming to tournaments. You practise less and just go and play matches. It's like the best-case scenario."

Sharapova has an excellent record in the Australian Open. She has reached the semi-finals or better in five of her last seven appearances and lost in the final in 2007 (to Serena Williams) and in 2012 (to Victoria Azarenka). When she won the title in 2008 she won every match in straight sets despite a draw that she describes as the toughest of her career, having had to beat Lindsay Davenport, Elena Dementieva, Justine Henin, Jelena Jankovic and Ana Ivanovic.

Sharapova now plays Ekaterina Makarova, the world No 19, in the quarter-finals for the second year in a row, having beaten her fellow Russian for the loss of only five games 12 months ago. Makarova, who saves her best Grand Slam performances for Melbourne, reached the last eight with a 7-5, 6-4 win over Angelique Kerber, the world No 5.

The winner of the all-Russian contest will meet Li Na or Agnieszka Radwanska in the semi-finals. Li, who beat Germany's Julia Goerges 7-6, 6-1, also has a good record here, having reached the last four in 2010 and the final in 2011.

However, there has been no player in better form this year than Radwanska, who beat Ivanovic 6-2, 6-4. Radwanska has won all 13 matches she has played in 2013 without dropping a set. The world No 4, who has reached three quarter-finals here but never gone any further, won both her warm-up tournaments, in Sydney and Auckland.