The Mets have been exceptionally frustrating this year – even more so than most .500 clubs. They have followed brilliant series with atrocious ones, watched their bullpen squander quality outings from their starting pitchers, and undermined their electrifying speed and power with a disconcerting lack of patience at the plate. For all that, the Mets sit only three games out of the wild-card spot after completing a weekend sweep of the Chicago Cubs with a 6-1 win last night at Shea Stadium.

The team simply looked done after last week’s series against the Milwaukee Brewers. Having recovered to win Tuesday’s game in the 11th inning after a 1 1/ 3 inning, six-run performance by starter Victor Zambrano, Willie Randolph’s bullpen promptly coughed up leads in the next two games. They gave up four runs in the last three innings of Wednesday’s game and suffered through Roberto Hernandez’s five run ninth-inning debacle in Thursday’s rubber match. The Mets managed to score 32 runs in the four-game series and won just one game in the process.

Being exceptionally frustrating, of course, the Mets looked like a pennant-winning team during the series against the Cubs. On Friday, the team whacked rookie Rich Hill for seven runs in 1 1/ 3 innings; the curveball specialist’s curve wasn’t curving, and the Mets took advantage, tagging him mostly with sharply hit singles. On Saturday, Jae Seo rewarded the loyalty of his faithful advocates by out-dueling Greg Maddux in a 2-0 classic that featured two starters throwing a hair above 83 miles per hour and Jose Reyes showing how he can take over a game with his speed. Coming off a five-game stretch during which they’d scored 40 runs, it was encouraging to see the Mets win a game despite Maddux lulling their bats to sleep. Considering that Mets’ pitchers had allowed 35 runs in that same stretch, it was equally encouraging to see them hold Derrek Lee and Aramis Ramirez, the Cubs’ terrifying nos. 3 and 4 hitters, to three hits in 16 at-bats.

But for a team that’s supporters have every right to be more than skeptical, last night presented an even tougher test, and that was Carlos Zambrano. The Cubs’ rather menacing ace hadn’t pitched less than seven innings or allowed more than three runs since June 28, and he is exactly the sort of pitcher who gives the Mets (and everyone else) fits.

Zambrano throws a 98 mph fastball high in the strike zone, and a low, 94 mph heater that no one can drive. He throws change-ups and sliders and slow curveballs for strikes, seems to enjoy coming up and in with his hardest stuff, and has only one real weakness, which is that he’s prone to getting a bit wild – a failing no Mets hitters save Cliff Floyd and David Wright are particularly good at exploiting. Further, as a sinkerballer, Zambrano doesn’t give up home runs, which figured to take away the Mets’ other signal strength.

But the Mets came out with a reasoned and consistent approach against Zambrano last night, becoming the first team in over a month to score more than three runs against him. Even better, they managed to knock him out of the game before the fourth inning.

The Mets have displayed throughout this season a somewhat irritating tendency to try to pull the outside pitch, a habit that leads to woe on the individual level and ineptitude on the team level. Last night there was none of it, but rather balls that were hit solidly up the middle, pulled on a line, and slapped the other way. The only way to get to a tough pitcher like Zambrano when he’s pitching well – and the man had his good stuff last night, and was putting it where he wanted it – is to go with the ball where it’s pitched, take some walks, and be aggressive on the basepaths, taking chances when they come.

While the Mets’ hitters were taking apart Carlos Zambrano, his namesake, the Mets’ Victor, was solid in pitching to the Cubs’ weaknesses. Zambrano was coming off the worst start of his career, and you might have expected him to change his usual approach of throwing a bunch of hard breaking balls just out of the strike zone. But given the Cubs hitters’ impatience, he was right to stick to his typical game plan, and he gave up just one run on five hits in eight innings.

Seeing the Mets do all this is a very good sign. They’ve won a slugfest and a pitchers’ duel and done well against the best of the Cubs’ impressive starting corps; with a bunch of sub-.500 teams coming up on the schedule, there’s no reason to think the run everyone’s been waiting for won’t finally arrive.

Another excellent sign at Shea this weekend was the play of Carlos Beltran, who’s finally hitting and running like the impact player the Mets thought they were signing this past winter. His hustle down the first-base line in the first inning last night forced third baseman Ramirez to make a throwing error; he then scored from first on a reasonably routine Floyd base hit to right-centerfield.

In so doing, Beltran looked like that rare player whose contributions really do include the vaunted “things that don’t show up in the box score.” The Mets have been reasonably good so far this year with their center fielder providing much less than was expected of him; the return of his aggressive, three-dimensional game is something like making a significant trade at the deadline and shouldn’t be underestimated in accounts of the team’s chances going forward.