If Theo Epstein needs help convincing teams that the right trade for the right pitcher can turn the right team into a contender, he can direct them to Nationals Park this weekend.

For all the attention that justifiably goes to Bryce Harper and Stephen Strasburg, it's possible that the key to putting the Nationals in first place in the National League East was winning the bidding for Gio Gonzalez last winter.

The Nationals gave up plenty to get Gonzalez from the A's. But they've since watched him turn into one of the most dominating pitchers in the league. They're 10-2 in his starts; add in their 11-2 record in Strasburg's starts, and the Nationals are 17 games over .500 when one of the top two in their rotation takes the mound.

They're under .500 in their other games.

"Best deal anyone made last winter," one rival scout said this week. "They didn't get him cheap, but he can dominate, and how many starters can you say that about?"

This is relevant this weekend because the Nationals are about to host the most exciting series in their history. They're the hottest team in the National League (six straight wins), and they're going to play the Yankees, the hottest team in the American League (six straight wins).

Meanwhile, Epstein's Cubs are hosting his former team, the Red Sox, at Wrigley Field. But if you past the Theo factor, it's just another chance for the Cubs to showcase a pitcher they're trying to trade.

Epstein has other teams know that the Cubs are already open for business, and that he plans to "be aggressive" in moving pitchers Ryan Dempster and Matt Garza. Reports out of Chicago indicate that Epstein has already talked to Dempster about possible destinations, an important step since Dempster has 10-5 rights and thus full no-trade protection.

Neither Dempster nor Garza looks to be the dominating game-changer that Gonzalez has become, but they're the best starting pitchers on the market right now. That could change if the Brewers make Zack Greinke available (possible, but probably unlikely), or if the Phillies make Cole Hamels available (even more unlikely).

In any case, the Nationals are the best example out there of what adding a big-time starter can do for a team. Trading for Gonzalez got them a weekend like this.

"The big, bad Yankees are coming to town," manager Davey Johnson told MLB.com. "Arguably, they're the best ballclub almost every year forever."

The Nationals are arguably the best ballclub now, coming off back-to-back sweeps in Boston and Toronto.

Since the current American League East was formed in 1995, only four teams have had back-to-back three-game road sweeps vs. AL East opposition. The big, bad Yankees have done it just once, against the Devil Rays and Orioles in 1999.

Since then, it happened with the 2000 Mariners (also against Baltimore and Toronto), with the 2011 Red Sox (at New York and Toronto), and with this year's Nationals.

It doesn't happen much. Series like the one the Nationals will host this weekend don't happen much.

Without the Gio Gonzalez trade, it probably doesn't happen at all.

On to 3 to Watch:

1. Dempster's 2.31 ERA is even better than Gonzalez's 2.35. Already, we know the Dodgers are interested, and other teams are no doubt interested, as well. Dempster could make himself even more attractive on the market with a strong outing in Red Sox at Cubs, Friday afternoon (2:20 ET) at Wrigley Field. Daisuke Matsuzaka is the starter for the Red Sox, interesting because how well he pitches over the next few weeks could help determine how big Boston's need is for another starting pitcher.

2. When he was with the A's, Gonzalez faced the Yankees five times. He lost the last four, allowing 20 earned runs in 19 1/3 innings for a 9.31 ERA. Gonzalez gets another chance in Yankees at Nationals, Friday night (7:05 ET) at Nationals Park. Many still expect the Yankees to be in the market for a starting pitcher, but if Friday starter Phil Hughes and Sunday starter Ivan Nova continue to pitch well, that need may not be glaring.

3. Two first-place teams meet in Washington. And two first-place teams meet in Los Angeles, in White Sox at Dodgers, Friday night (10:10 ET) at Dodger Stadium. As just as Gonzalez is a big reason that the Nationals are in first place, Friday night starter Clayton Kershaw is maybe the biggest reason the Dodgers are there. For that matter, Friday night starter Chris Sale is one of the biggest reason the White Sox are there.