CHICAGO, IL, USA - No.3 seed Zarina Diyas was the highest-ranked winner on the first day of the inaugural Oracle Challenger Series Chicago, coming from a set down to take control against Kateryna Kozlova 3-6, 6-2, 6-1 to book her place in the second round.

A left knee injury sustained in Nottingham had forced the Kazakh to miss the rest of her beloved grass court season, returning only in Cincinnati, where she fell in the qualifying rounds. However, Diyas has been finding form again since, qualifying and winning a round in New Haven before taking a set from Petra Kvitova; at the US Open, she pushed another Top 10 player hard, forcing Karolina Pliskova to save four set points to eventually win 6-4, 7-6(4).

Two other seeds were stretched to their limits in Chicago. No.6 seed Sachia Vickery pulled through 6-4, 4-6, 6-4 against the mercurial talent of Ons Jabeur to seal her first main draw win since Wimbledon, while No.8 seed Johanna Larsson outlasted Beatriz Haddad Maia 6-4, 1-6, 7-6(3) after two hours and 21 minutes, saving three match points en route.

The Brazilian has had more than her fair share of injuries in her young career, and is playing just the third tournament of a comeback from a back problem that had kept her sidelined since Madrid. The 22-year-old served for the match at 5-4 in the third set against Larsson, and even after failing to take three match points in that game would still take a 3-0 lead in the deciding tiebreak.

However, the Swede - who took Wimbledon champion Angelique Kerber to three sets at the US Open last week - would again refuse to give in, and reeled off the final seven points of the match to seal victory.

Elsewhere, No.4 seed Tatjana Maria continued her resurgent form with a 7-5, 6-3 defeat of qualifier Irina Falconi; wildcard Allie Kiick notched up the fourth Top 100 victory of her career with a 6-7(3), 6-2, 6-2 upset of Kristyna Pliskova; and former World No.23 Mona Barthel came from a set down to overhaul Zhu Lin 5-7, 6-2, 6-4.

The most emphatic win of the day was Madison Brengle's 57-minute 6-0, 6-0 rout of wildcard Lauren Davis - the 28-year-old's first double bagel victory in a WTA event, and her first at any level since beating Zuzana Zlochova in the first round of the 2013 ITF $25,000 in Surprise without losing a game. Brengle conceded just six points in the first set, but four of the second set's six games were lengthy deuce tussles.

TUESDAY'S ORDER OF PLAY (all courts start 10am)

COURT 1
Eugenie BOUCHARD (CAN) vs [Q] Kristie AHN (USA)
After 1 ATP match
[1/WC] Danielle COLLINS (USA) vs Jana FETT (CRO)

COURT 2
After 1 ATP match
[Q] Jamie LOEB (USA) vs Petra MARTIC (CRO) [2]
After 1 ATP match
Katie BOULTER (GBR) vs [WC] Varvara LEPCHENKO (USA)

COURT 4
Veronika KUDERMETOVA (RUS) vs [Q] Sesil KARATANTCHEVA (BUL)
Anna BLINKOVA (RUS) vs [WC] Francesca DI LORENZO (USA)
Mona BARTHEL (GER) / Kristyna PLISKOVA (CZE) vs Natela DZALAMIDZE (RUS) / Veronika KUDERMETOVA (RUS) [4]
Jamie LOEB (USA) / Sachia VICKERY (USA) vs Alexandra MUELLER (USA) / Emily WEBLEY-SMITH (GBR)

COURT 6
Dayana YASTREMSKA (UKR) vs Pauline PARMENTIER (FRA) [5]
Evgeniya RODINA (RUS) [7] vs Sara SORRIBES TORMO (ESP)
Beatriz HADDAD MAIA (BRA) / Ons JABEUR (TUN) vs Elena RYBAKINA (KAZ) / Karman THANDI (IND)
Alexa GUARACHI (CHI) / Desirae KRAWCZYK (USA) [3] vs Michaella KRAJICEK (NED) / Pauline PARMENTIER (FRA)