| Date: | September 4–9 |
| Edition: | 1st |
| Draw: | 32S / 16D |
| Surface: | Hard, outdoor |
| Prize Money: | $150,000+H (ATP) $150,000 (WTA) |
| Category: | ATP Challenger Tour WTA 125K series |
| Location: | Chicago, United States |
| Venue: | XS Tennis Village |
| Champms: |  Denis Istomin |
| Champmd: |  Luke Bambridge / Neal Skupski |
| Champws: | Petra Martić |
| Champwd: | Mona Barthel /  Kristýna Plíšková |
| After Year: | 2021 |
| After Name: | Chicago Challenger |
The 2018 Oracle Challenger Series – Chicago was a professional tennis tournament played on outdoor hard courts. This tournament was part of the 2018 ATP Challenger Tour and the 2018 WTA 125K series. The first edition took place from September 4 to 9, 2018 in Chicago, United States.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Italy | Andreas Seppi | 51 | 1 | |
| Uzbekistan | Denis Istomin | 76 | 2 | |
 Canada | Vasek Pospisil | 88 | 3 | |
 Serbia | Viktor Troicki | 102 | 4 | |
| Michael Mmoh | 120 | 5 | ||
 Belgium | Ruben Bemelmans | 128 | 6 | |
 Sweden | Elias Ymer | 132 | 7 | |
| Noah Rubin | 135 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry into the singles main draw as alternates:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Danielle Collins | 37 | 1 | ||
| Petra Martić | 47 | 2 | ||
 Kazakhstan | Zarina Diyas | 60 | 3 | |
| Tatjana Maria | 70 | 4 | ||
 France | Pauline Parmentier | 71 | 5 | |
| Sachia Vickery | 78 | 6 | ||
 Russian Federation | Evgeniya Rodina | 80 | 7 | |
| Sweden | Johanna Larsson | 82 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry from the qualifying draw:
Jennifer Brady → replaced by 
Duan Yingying Dalila Jakupović → replaced by 
Beatriz Haddad Maia Vania King → replaced by Zhu Lin 
Magda Linette → replaced by Madison Brengle Christina McHale → replaced by Jana Fett 
Monica Niculescu → replaced by Katie Boulter Rebecca Peterson → replaced by Mona Barthel Monica Puig → replaced by 
Ons Jabeur| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
| Kaitlyn Christian | Sabrina Santamaria | 108 | 1 | |||
| Darija Jurak | Xenia Knoll | 128 | 2 | |||
| Alexa Guarachi | Desirae Krawczyk | 154 | 3 | |||
| Russian Federation | Natela Dzalamidze | Russian Federation | Veronika Kudermetova | 182 | 4 |
See main article: article and 2018 Oracle Challenger Series – Chicago – Men's singles.
Denis Istomin def. Reilly Opelka 6–4, 6–2.See main article: article and 2018 Oracle Challenger Series – Chicago – Women's singles.
See main article: article and 2018 Oracle Challenger Series – Chicago – Men's doubles.
Luke Bambridge / Neal Skupski def. 
Leander Paes / 
Miguel Ángel Reyes-Varela, 6–3, 6–4See main article: article and 2018 Oracle Challenger Series – Chicago – Women's doubles.
Kristýna Plíšková def. Asia Muhammad / Maria Sanchez, 6–3, 6–2
