The rare North Side-South Side swap landed the defending champs a top-flight starter and the rebuilding Sox even more top prospects. Patrick Gorski-USA TODAY Sports

The oft-suggested notion that the White Sox and Cubs won’t do a high-profile trade together has, on its surface, always been absurd.

There are only 29 potential trade partners around, and if a deal helps your team, who cares if it also helps your in-market competitor?

Anyway, the two Chicago franchises set that theory on its ear Thursday with an out-of-nowhere trade: The White Sox sent lefty starter Jose Quintana to the Cubs in exchange for another impressive prospect haul for ChiSox GM Rick Hahn, including outfielder Eloy Jimenez (the No. 5 overall prospect per ESPN's Keith Law) plus pitcher Dylan Cease and infielders Matt Rose and Bryant Flete.

According to ESPN Stats & Information, this is the first all-Chicago trade since November 2006, when the White Sox sent Neal Cotts to the Cubs for David Aardsma and Carlos Vasquez. But it’s the highest-profile deal between the teams since the White Sox sent a young Sammy Sosa and pitcher Ken Patterson to the Cubs for George Bell in 1992.

The Cubs’ need for starting pitching help has been well-chronicled.

The defending champs rank No. 26 in starting pitcher WAR at the break and have the worst first-inning ERA of any staff. (Quintana’s first-inning ERA of 5.00 won't help in that regard if it continues.) The Cubs limped into the break at two games under .500, and they trail the NL Central-leading Milwaukee Brewers by a season-high 5.5 games, so clearly there was an urgency to get a jump on what is expected to be a slow-developing trade deadline season.

Quintana, 28, has been one of the most durable and consistent starters in baseball over the past four years, posting a 3.35 ERA from 2013 to 2016 while averaging 204 innings per season. He has recovered from a slow start and likely slots between Jake Arrieta and John Lackey in the Cubs’ revamped rotation, which should line up something like this: Jon Lester, Arrieta, Quintana, Lackey and Kyle Hendricks, who is expected to return from the DL shortly after the break. The addition of Quintana will allow the Cubs to shift Mike Montgomery back to the long-relief and occasional No. 6 role he had been slated for.

Cubs Starting Pitchers This Season ERA Starts Eddie Butler 3.86 11 Kyle Hendricks 4.09 11 Jon Lester 4.25 19 Jake Arrieta 4.35 18 John Lackey 5.20 17 Mike Montgomery 5.40 6 Brett Anderson 8.18 6 >> Cubs: 4.66 starters ERA (Eighth in NL)

As strong as Quintana’s performance has been, his contract was another key aspect of the deal. The Cubs will have team control over his contract beyond this season, which served to drive up his trade value for the White Sox. Quintana will earn just $6 million this season, $8.4 million in 2018 and $10.5 million in both 2019 and 2020, and during those last two seasons, the Cubs will hold a $1 million buyout option, per ESPN Stats & Info. Having that kind of consistent production at such a low fixed price point is invaluable for the Cubs’ front office, which will need to lock up some of its younger in-house talent over the next few years, while also possibly getting involved in the promising free-agent market of 2018 that is expected to include Bryce Harper, among others.

Losing Jimenez is a blow for the Cubs and president Theo Epstein, but the organization already has a young outfield at the big league level: Kyle Schwarber, Ian Happ, Albert Almora and Jason Heyward. And, again, there is always the free-agent marketplace.

The White Sox hit the reset button at the winter meetings in December, ostensibly embarking on the organization’s first full-blown rebuild in eons. Hahn dazzled the industry at the start of that process. First, he landed top prospects Yoan Moncada and Michael Kopech, plus outfielder Luis Alexander Basabe and pitcher Victor Diaz, from the Red Sox in exchange for ace lefty Chris Sale. Then Hahn followed up strong, sending center fielder Adam Eaton to the Washington Nationals for pitching prospects Lucas Giolito, Reynaldo Lopez and Dane Dunning.

In doing so, Hahn laid the groundwork for Thursday’s deal, if only by establishing the kind of return he’d require for his biggest remaining trade chip in Quintana. The White Sox shot up the prospect rankings after the winter deals, but the reset project seemed stuck in limbo, and only a Quintana-themed blockbuster would complete the picture. And indeed it has, though it took eight months to happen. Waiting carried risk for Hahn, and we all knew it: What if Quintana got hurt or simply floundered?

At the beginning of the season, it appeared the latter may be true.

Quintana stumbled out of the gate. Through the end of May, he was just 2-7 with a 5.60 ERA. Nevertheless, even then, the whispers were that his trade value had not really been impacted by the short-term struggles. Still, it can’t have hurt that since the beginning of June, Quintana has gone 2-1 with a 2.70 ERA over seven starts. Thursday’s deal made clear what the industry suspected: Quintana’s value was very much intact.

Jose Quintana This Season April-May June-July W-L 2-7 2-1 ERA 5.60 2.70 WHIP 1.40 1.20 Opp BA .265 .213 Opp OPS .802 .622

The White Sox system is now fairly well-loaded with near-ready MLB talent. Law’s newest Top 50 now includes a gaggle of future South Siders, led by Jimenez at No. 5. After him are No. 7 Kopech, No. 13 Moncada and No. 17 Giolito. With the Quintana issue resolved, the White Sox can turn their attention to dealing closer David Robertson and possible other bullpen trade candidates such as Tommy Kahnle and Anthony Swarzak, not to mention third baseman Todd Frazier. Any prospects Hahn adds from here on out will be gravy, and given the number of possible future stars he has in the upper rungs of the minors, he can target younger, high-upside, high-risk prospects in other deals if he wishes.

All in all, this trade makes a lot of sense for both sides. That the South Siders and North Siders were able to traverse that old public relations maze, which might have prevented previous intra-Chicago trades, is to the credit of both organizations. This year’s interleague matchup between the teams, which takes place from July 24-27, will be that much more interesting because of this deal. But the possibility of even higher-level matchups sometime down the line is even more intriguing.