SAP Inside the Numbers is an ongoing series which looks to preview and reflect on the tour's major swings throughout the season.

The North American summer hardcourt season is in the books and the tour is set to transition over to Asia for the remainder of the season. SAP and WTA Insider dig int other numbers behind the six-week summer series, which saw No.1 Simona Halep dominate the tour until 20-year-old Naomi Osaka broke through to win the US Open. 

Naomi Osaka became the 1st Japanese player, man or woman, to win a Slam singles title. (Getty Images)

US Open: Naomi Osaka d. Serena Williams, 6-2, 6-4.

Simona Halep is now 10-0 when the Rogers Cup is hosted in Montreal. (Getty Images)

Montreal: Simona Halep d. Sloane Stephens, 7-6(6), 3-6, 6-4
Cincinnati: Kiki Bertens d. Simona Halep, 2-6, 7-6(6), 6-2 (saved MP)
New Haven: Aryna Sabalenka d. Carla Suárez Navarro, 6-1, 6-4
San Jose: Mihaela Buzarnescu d. Maria Sakkari, 6-1, 6-0
Washington D.C.: Svetlana Kuznetsova d. Donna Vekic, 4-6, 7-6(7), 6-2 (saved 4 MPs)

World No.1 Simona Halep leads the tour in both overall match wins (46) but also hardcourt wins this year, tallying a 28-5 record this season. Halep's hardcourt summer included an astounding two-week run through Montreal and Cincinnati, which saw her play 10 matches in 12 days and win 9 of them to win Montreal and make the final in Cincinnati. 

The hardcourt summer also saw the emergence of 20-year-old Aryna Sabalenka. The 20-year-old Belarusian went 14-3 in North America, scoring 5 Top 10 wins (d. Wozniacki, Kvitova, Pliskova, Goerges), and winning her first WTA title in New Haven. Sabalenka rode that momentum to her 1st Round of 16 appearance at a Slam, where she was the only player to take a set off the eventual champion. Prior to the summer, Sabalenka had just one Top 5 win in her career. 

Finally, the Netherlands' Kiki Bertens laid down an unexpected marker on hardcourts. Famously self-described as a clay-court specialist, Bertens came into the summer having never defeated a Top 10 player on hardcourt, let alone make a hardcourt final. Over the span of 2 weeks, Bertens notched 6 Top 10 wins, including four such wins en route to her first hardcourt title in Cincinnati, where she defeated No.1 Halep in the final. 

En route to her first major title, Naomi Osaka was near-unbreakable in New York, holding serve in 91.5% of her games, an increase of 17.8% over her season average and 11.2% over her title-run at Indian Wells this year. 

The 20-year-old saw her serve broken just 5 times through 7 matches, and her serve came up big when she needed it the most. Against 2017 US Open finalist Madison Keys in the semifinals, Osaka saved an astounding 13 of 13 breakpoints and was broken just once by Serena Williams in the final. 

"I think whenever I had a breakpoint, she came up with some great serve," Williams said after the final. "Honestly, there's a lot I can learn from her from this match."

Keys echoed similar praise for Osaka's ability to withstand the pressure. "It's obviously tough because you keep fighting, trying to get the breakpoint, then for her to come up with some of the shots, it was difficult," said Keys. "But you're in that match and you think, Okay, she's going to let up eventually. She didn't. All credit to her."

Osaka has now won two of four of the tour's biggest hardcourt titles in 2018 (Caroline Wozniacki won the Australian Open, Sloane Stephens won Miami). While she may have been quiet during the clay and grass seasons, she has steadily improved her success rate on service and returns. When Osaka is firing she has been dominant. In both her title runs in Indian Wells and the US Open, Osaka lost just one set.

As a result of Osaka's improvements, she has skyrocketed into the Top 10 for the first time in her career. She is the highest-ranked Japanese woman since Kimiko Date in October 1996.

When it comes to measuring the dominance of Osaka's serve, it's important to note her "strikeout" rate. Coming into the 2018 season, Osaka had recorded 8 instances of not being broken in a match. Through 9 months of this season, Osaka has done it  a tour-leading 10 times. 

More Summer Hardcourt Notes:

-  The 2018 US Open final was the second-widest age gap between finalists at any Slam in the Open Era. 16 years separated 36-year-old Serena Williams and 20-year-old Naomi Osaka.

- For the 1st time in 80 years, back-to-back seasons have produced 8 different major champions. 

Serena Williams (Australian Open) 
Jelena Ostapenko (Roland Garros)
Garbiñe Muguruza (Wimbledon)
Sloane Stephens (US Open)

Caroline Wozniacki (Australian Open)
Simona Halep (Roland Garros) 
Angelique Kerber (Wimbledon)
Naomi Osaka (US Open).

- Julia Goerges continues to lead the tour in aces, firing 393 over 54 matches. Her lead over Karolina Pliskova has stretched out to nearly 100 aces (Pliskova has hit 299). Kiki Bertens (246), Kristyna Pliskova (244), and Ashleigh Barty (242) round out the Top 5. 

- Serena Williams has overtaken the top of the leaderboard when it comes to the most dominant serve in tennis. Julia Goerges and Ashleigh Barty have spent the season jockeying back and forth at the top of the serve stats, but after her 2nd consecutive run to a major final in New York, Serena is part of the mix. 

The American leads the tour in 1st service points won (74.4%) and service points won (63.8%).

- Kiki Bertens...does not love tiebreaks. Bertens has played 20 tiebreak sets this year, a tour-best, but has won just 7 of them (35%). In her 3-set loss to 19-year-old Marketa Vondrousova in the third round of the US Open, Bertens lost two tiebreaks to bow out early.

- The most aces hit in a single match during the summer hardcourts was 18, struck by Serena Williams in a three-set Round of 16 win over Kaia Kanepi at the US Open, and Viktoria Kuzmova in Cincinnati, en route to a win over Aliaksandra Sasnovich.

- The longest match of the summer hardcourt season goes to the contrast of styles between Dominika Cibulkova and Hsieh Su-Wei. The two battled it out for 3 hours and 19 minutes in the second round of the US Open. Cibulkova won 7-6(3), 4-6, 6-4.

- Naomi Osaka is now 32-0 when she wins the 1st set of a match this season.

- In her first 25 Slam finals, Serena Williams posted a 21-4 record (through 2015 Wimbledon). Since then, she is 2-4 in Slam finals.