You can debate the merits of expanded rosters in September, like my colleague Bill Parker did on Getting Blanked yesterday. Or you can marvel at how one player added to a roster on September 1 can immediately make a big difference for a contending team. Since the Impact Index is all about marveling at the difference one player makes in a particular game or week, we’re going to go with Option Two.

We’ll start with The Prospect. The Texas Rangers called up Jurickson Profar on Saturday. As Scott Lewis wrote, Profar is a highly touted and toolsy young middle infielder who hits for average and power, gets on base, runs fast and has a smooth glove. And I mean young. The first player born in 1993 to play in a Major League Baseball game.

On Sunday, he was the starting second baseman for the defending American League Champions in a game against the Cleveland Indians thanks to Ian Kinsler’s stiff back. With the score tied 0-0 in the top of the 3rd, Profar walked to the plate for his first major-league at-bat. On a 2-1 count, he deposited a 90-mph fastball from Zach McAllister into the right field seats at Progressive Park. Click here to watch it. It launched a four-run inning for the Rangers, who went on to beat the Indians 8-3. Welcome to the bigs.

Also on Saturday, and again on Sunday, uber-gritty veteran Xavier Nady came through in a big way for the San Francisco Giants. What’s that? You’re wondering why we’re profiling a veteran in a story about September call-ups? Well, Nady’s been playing with the Giants’ Triple-A team since early August, after the Washington Nationals released him earlier this season. Yes, it’s the same Xavier Nady we profiled back in April, when he was getting clutch pinch hits off the bench for the Washington Nationals. That clutchness didn’t last long, however, as Nady posted a .157/.211/.275 slash in 109 plate appearances with three home runs. The Nationals released him in July.

With Melky Cabrera suspended for the rest of the season, the Giants have been casting about for a left fielder who can hit a little and field a little. That led to Nady’s call up on Saturday, and his place in the starting lineup against the Cubs. Nady is a native of the San Francisco Bay Area and he played college ball for the University of California, Berkeley. In his first plate appearance for his hometown team, Nady batted with the bases loaded and two outs. He did this:

Those proved to be the winning runs in the Giants’ 5-2 victory over the Cubs. Nady followed that up on Sunday with two hits, two walks and two runs scored as the Giants came from behind to beat the Cubs and complete a 5-1 roadtrip.

Another, more traditional September call-up played a big role in the Giants’ win on Monday against the Arizona Diamondbacks at AT&T Park. Right-handed reliever Jean Machi has bounced around the minor leagues for eleven seasons, spending time with in the Phillies, Rays, Blue Jays, Pirates and Giants’ farm systems. The Venezuelan native spent this season with the Giants’ Triple-A team, throwing 56 2/3 innings out of the bullpen, mostly as the closer. The Giants called him up on Saturday and at age 30, he made his big-league debut on Monday.

Machi pitched the 8th inning for the Giants, retiring Paul Goldschmidt, Miguel Montero and Chris Johnson on two pop ups and a ground out to short. Not terribly remarkable, except the Giants hurlers who pitched in the game before Machi hadn’t been successful in retiring those Diamondbacks, or most others. Starter Barry Zito, and relievers Guillermo Mota, George Kontos, and Shane Loux had coughed up eight runs to the Diamondbacks through seven.

However, Machi held the line, giving the Giants a chance to come back from an 8-5 deficit. They seized that chance, scoring two in the bottom of the 8th, one in the bottom of the 9th, and one in the bottom of the 10th for a thrilling 9-8 victory. With the back end of the Giants’ bullpen leaking oil as the try to close out the National League West division title, we should expect to see a lot more of Jean Machi down the stretch.

There was one other notable performance by a September call-ups over the weekend, although it was in a losing effort. Brock Holt debuted with the Pittsburgh Pirates on Saturday, drawing a walk in a pinch hit appearance and scoring. He started at second base for the Bucs on Sunday, going 2-for-5. Holt’s efforts were not enough, as the Pirates lost both games, and again on Monday, pushing their losing streak to four games. Pittsburgh now sits 2 1/2 games behind the St. Louis Cardinals for the second wild card in the National League.

Thirty more days. That’s all that’s left in the 2012 regular season. More September call ups are on the way. Some will make a big impact on the tight division and wild card races. We’ll be watching.